I guess one could argue that given that it was possibly a commission sale, that the shop had a duty to get the best price for their customer.
That should have been sorted out before it went up for sale though. I say 'sale', but it sounds like it was a blind auction.
I'd also argue the case for the buyer saying 'I understand it's sold, but let me have first refusal if things don't work out'.
But, 'I don't care if it's sold, I'll give you more money, plus you won't have to ship it internationally' sucks big time from both sides.
I have visions of there being a mirror thread on Talk Bass.