It goes without saying that almost all the instruments that find their way into my workshop are in some state of disrepair - and that my job largely consists of diagnosing the faults and repairing them.
However, there are times when the matter in hand isn't so much about what's wrong the instrument but how it got like that in the first place.

In these cases there's nearly always a common factor - that of the instrument being out of the care of the owner, whether it be left in storage somewhere or placed in the trust of someone else...most typically a shipper or the postal service. The instrument leaves the care of the owner in good condition, and is returned damaged in some fashion.
Another common factor is that the instruments are almost all saxes; flutes and clarinets etc. are small and light enough to cope with a few knocks, and usually only exhibit damage if severely mistreated.
It then falls to me (perhaps an unfortunate choice of words) to inspect the instrument and speculate as to how any may have damage occurred. This can either be an informal process - simply to satisfy the client's curiosity or bemusement - or a formal one, usually as part of an insurance claim.
It's a particularly interesting facet of my job, and one that requires quite a thorough examination of both the instrument and its packaging.

In terms of an insurance claim all that's really needed is an answer to the 'whodunnit' question. Someone is deemed to be responsible, it's my job to look at the evidence and present the most likely cause of damage - from which it can be deduced who gets to pay the bill.
There are times though when it's just as important to establish how the instrument was damaged, or where, when and why (a howdunnit, wheredunnit, whendunnit and, well, you get the gist). This is more likely to be of interest to the client when an instrument gets damaged in storage - which supposes a deliberate act rather than an accident.

In a very few cases the evidence points to deliberate damage on the part of the owner - and this is always indicative of either a client who's dropped the instrument and is too embarrassed to admit to it (I usually get them to 'fess it up' in the end - it's good Karma) or a young student who perhaps would prefer to be doing other things rather than learning to play an instrument.

There are three main types of damage seen on a cased instrument; Shock damage, impact and crush damage. Each type has a particular 'signature'.
Shock damage result from a cased instrument being dropped. This doesn't always leave marks on the case, and tends to exhibits itself on the instrument in the form of gentle bends to the metalwork and large dents underneath protruding keys and fittings.
Impact damage, where something has hit the case, is more localised, and often shows evidence of damage to the case. The damage to the instrument is often confined to one area, and can be quite severe.
Crush damage is nearly always devastating - both case and instrument are usually severely damaged. Tyre tracks are sometimes in evidence!
Naturally, there's some crossover in the damage type. A case falling from a height and landing on one of its corners will result in impact damage, for example - and often shock damage too.

It's usually relatively easy to tell what has happened to an instrument by the nature of the damage - a skill that comes from seeing countless similarly damaged instruments where the owner claims full responsibility and is able to describe how it happened in detail.
Thus, for a sax with a bent bell lip (with no scratches to the bell), a dent in the bell under the bell stay joint and a slight forward bend in the body, with perhaps some damage around the G/G# tone hole would indicate that the sax was dropping in its case with the bell facing the floor. A vintage horn, with a small, thin bell brace will usually also have a hefty dent where it meets the body, and the toneholes either side of it will be badly distorted.
Scratches to the bell around the creased and bent lip would indicate the horn it a hard surface - so wouldn't have been in its case when it hit the deck (though it's as well to check the case for anything that might have caused the scratches).

The client is often present when I make my examination, and this can lead to some startling revelations for them.
A recent example was a Selmer alto that had severe damage to its low Eb guard, and only the guard, on its return from a spell in the company of baggage handlers.
Such was the nature of the damage that it would be extremely unlikely that the force required to distort the guard so badly wouldn't have left visible damage elsewhere (this usually occurs when case is dropped on it its hinges - most case have the rear of the sax facing the hinges).
The specific damage was unusual too - when a guard cops a whack it usually folds flat, but this guard had a visible groove in it along with scratches around the groove. This couldn't have happened while the horn was in the case - the pattern of damage, the groove, the scratches and the lack of any other damage point to this horn having been taken out of its case and then damaged somehow.
Likely scenario? Someone opened the case in transit, got the horn out of the case and was swinging it about a la 'look at me, I'm a sax player'. In the course of a backward swing the horn hit a table, or some other object with a neat edge.
Just a guess, of course - but quite clearly the horn was damaged outside the case, and in a very specific manner.

There are times though when even I'm beat.
The most recent example concerned a straight soprano sax. This was brought in by a retailer who'd had the horn returned under warranty with an accompanying note that told of problem with the low notes. A second note from a teacher confirmed the problem.
On opening the well-wrapped case the retailer discovered all the bell keys hanging off, and noticed that the bell key upper pillar had been knocked some considerable distance out of line.

The most obvious conclusion was that it couldn't have been sent out like this in the first place - the retailer would certainly have spotted the keys hanging off the horn - so it was transit damage.
However, the sax case was one of the semi-soft variety. These cases are rather good - they have a dense foam or polystyrene interior which gives excellent shock protection and a hardboard shell (covered with a black synthetic material) that gives good impact and crush resistance. These cases are light and portable, though less resistant to general wear and tear than a full hard case.
I was sceptical that the horn could have taken such damage whilst in its case ; the bell key pillar was a substantial piece of brass, and a force transmitted through the case sufficient to bend this pillar would have left a lot of collateral evidence.

My first test then was to check the clearance between the top of the bell key pillar and the case lid.
I did this by placing a mound of blu-tak on top of the pillar, raising it and shutting the lid until such times as the lid deformed the mound. By this method I determined that there was about 18mm clearance.
This would mean that an impact to the lid would first have to deform it by 18mm before the lining of the case touched the pillar.
Had it done so, the stiff foam would have received a dent. This is easy enough to test for - simply find a flat spot in the case and poke a fingernail into the lining. It leaves a dent - and I would have expected to have found one immediately above the bent pillar. There was no dent though.

It was increasingly looking like the damage had been sustained outside of the case - which suggested 'operator error' (a polite way of saying the player dropped the horn), and in such instances it's often less hassle for the retailer to have the problem fixed and return the goods rather than waste time arguing about who's at fault, and chalking the bill up to expenses.
And so the horn was repaired and returned - but not before I'd tested the effectiveness of the case by putting the horn in it and knocking it against a few doors and table legs.

A week or so later I was extremely surprised to have an email forwarded to me by the retailer from the owner of the horn. Apparently it still wasn't working - and there was a rather 'frank' note from the player's teacher that wasn't at all complimentary.
This was getting to be very suspicious indeed.

On collecting the horn I found exactly the same damage as before - with the bell key pillar knocked out of line and half the bell keys hanging off. The retailers instructions this time were to 'test to destruction' - which effectively means do absolutely anything to replicate the damage. I was being paid to wreck a horn!
The thing was - how? I couldn't just take a hammer to it, I had to find out exactly what caused the damage. Was it a case of a disgruntled buyer deliberately sabotaging the instrument, or was there really something about the design of the horn or the case that led to the damage? To be honest it was a tough one to call, given that the retailer had sent out a great many similar horns and not had a single one back like this one.

So, I once again repaired the damage and prepared to do whatever it took to break the horn again.
My first test was to give the pillar a good clout. I knew that this would undoubtedly bend the pillar, but I'd have to hit the pillar in a particular spot and unless I was particularly careful it would leave an impact mark. I simply couldn't imagine anyone going to all the trouble to do this - and in any event, when I did the test I found that it didn't bend the pillar in quite the same way.
Once again I realigned the pillar and replaced the keys.
I then set about jumping on the case. This didn't have any effect at all...so I gave it a couple of hefty kicks. Again, no effect.
I threw it around the workshop for a while - no effect.
I then decided to be a bit more methodical by dropping the case onto each of its sides, one by one - first the top, then the bottom, then the sides...
Nothing happened...until I dropped the case on its end, specifically the mouthpiece end.
The results were dramatic. Dropping the case from head height straight onto the end resulted in the bell key pillar being knocked clean out of line! I'd found the problem. I repeated the test a few times and found that the minimum height at which damage was sustained was at about chest height. A drop from any lower than that didn't have any effect, neither did swinging the case into a wall - unless you really, really gave it one hell of a swing (and then you'd rightly expect some damage - and that effectively comes under the 'operator error' heading). I also found I had to drop the case dead square onto its end - a drop at even a slight angle (onto a corner, for example) didn't result in any damage.

What was causing the damage was 'hammer action'. As the case accelerates down towards the floor it stores energy. Once it hits the floor inertia is translated into force, and the combined weight of the bell keys hurtles forward into the pillar like a hammer, thus deforming the pillar.
At some point during the horn's journey the case had taken a whack 'end on' - and this had happened on two separate occasions. Clearly the chief suspect is the courier - but much as we often moan about the way our parcels are handled I find it hard to believe that a courier would deliberately drop a package from head height, twice, in the same fashion. I suppose, at a pinch, you might suppose that the courier knew the parcel contained a soprano sax, and that they had some peculiar vendetta against the instrument....perhaps as a result of living next door to someone who played Kenny G albums at all hours of the night...
Seems unlikely though.
I rather suspect the answer is more mundane.
The most likely cause of the damage is the horn sliding about in the back of a van.
In a well-packed van there would be other parcels in the load space - but at some point or other most of these parcels will have been delivered...leaving a great deal more space. It's possible then that the horn was able to move about (perhaps it was even the last package to be delivered on both occasions). Even the smallest van has at least five feet of floor space - and I suggest that in the process of accelerating and braking the horn had slid that five feet across the van's floor and crashed into a solid wall - and let's be frank here, courier drivers aren't exactly noted for their propensity to drive around in a slow and sedate manner. In an empty van there's a very good chance that the parcel would have ended up aligned with one of the sides - thus ensuring that when it eventually slid across the floor it would have hit a well end-on.

That, my friends, is my theory - and I'm sticking to it.
There is, however, one remaining mystery.
Clearly the horn was damaged when it arrived at the buyer's house - and on both occasions the complaint was that the low notes didn't work. This point was made quite clear in the teacher's email.
The mystery is - how on earth could anyone not notice that the bell keys were hanging off?