A few years ago I studied cracks.
I recall a customer said that as their daughter was playing they heard a snap, and then the instrument did not respond well.
After setting it aside for a while they played it again and the instrument played fine. For about 10 minutes.
This then brings up the science of how a crack is created (in one specific instance) ==>
http://clarinetperfection.com/WhyCrack.htm
Essentially, a cold body clarinet, when starting to play, the internal bore temperature increases dramatically fairly quickly. that puts pressure on the outside thickness of the instrument.
I recreated the scenario on a tube of wood put in the freezer for a bit to bring the temp down. Then I had a hot air gun shoot inside the instrument. I was able to crack the wood tube. Repeat on the other side and repeated a crack. I wish I took the internal and outside surface temp. Oh well.
If the outside temperature is cold and it is compressed it will hold the inside from expanding.
For a while until the outside temp, of the wood expanding reaches a certain temp, then the inside pressure pushing out greatly exceeds the outside pressure maintaining the pressure going inside. Then "snap" the outside dimension cracks.
The above link, I was able to repeated have the outside open up.
This is consistent with players saying everything works fine for 10 minutes (or some amount of time) then the instrument stops responding. The inside pressure then opens up the outside crack.
As to values ... well, a damaged clarinet I basically put at half of it's "as-is" market value. This was shown consistent when I did some valuation research a few years ago ==>
http://clarinetperfection.com/ClarinetValue.htm
After all. Would you buy a car that has 10 miles on it in perfect condition.
or a car with 10 miles on it that was crashed, junked, but someone rebuilt it to "perfect" condition ?
and how would you value those two EXACT same cars ?
It's just one of those things. Just play a plastic clarinet because it is less to worry about.
I subbed in an outdoor concert before, on clarinet. I played my B12.
Other woodwind players had intonation issues of their horns being in the bright evening sun on a hot summer evening. The plastic clarinet just minimized potential issues for me.
Fixing a crack I've found is more than just using pins. One must seal the crack - through glue - to keep the seal totally closed.
Think of it this way too. If you have a crack going into a tonehole slightly cracks opening in the tonehole will create a bypass to the pad an viola, the instrument won't be able to maintain airtightness anymore.
I had another example where the crack was a LAYER in the wood close to the bore. as it slightly expanded it created a very small chamber which was essentially a crack and the instrument wouldn't play well.
Cracked instruments bring about the uncertainly of the instrument thus they are valued much less by the player.
Retail places add their work to the instrument so their prices will be higher than an open market sale. think of it as custom motorcycles or cars. The first owner pays a premium for custom work, the 2nd owner doesn't care and the first owner uses looses a bunch of original purchase price money.