it looks like a wood issue honestly. Some woods are more natorious for this than others. It really looks like the crack is following the heartwood/sapwood line which likely spells trouble!
Its not the crack I'm used to seeing (right in the corner where the shelf-site window meet, and I have yet to have a good answer for this problem also)! I've had a number of higher end bows crack in that corner both front and/or back on the bow, all hairlines on both bows from well known bowyers and small time boywers. Not one has had a good explination for it. One refunded 2 bows on order and the third that cracked stating I would NEVER be happy, which was highly dissappointing, others I picked up used and they either developed the crack (on newer bows) or had it on older ones.
If that crack is following the grain it could likely be a bad failure in the making. It likely didnt happen at the post office unless your postal worker went...well, postal and wrapped it around something.
If you can open it up, you could force thin epoxy or ca glue down it...and pin it on either end of the crack to stop it from moving. but it doesnt resolve a potential inner flaw in the wood. the best answer is to send it back or hang it up on the wall.
In the end, I wouldnt blame a bowyer for this one by the picture alone, atleast in my eyes, that crack hits the heartwood/sapwood area and follows it. bowyers are good, but they're not miracle workers
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