well that sucks!
but yeah I don't find the OP at fault, to me he did the honorable thing
it was the guy that had the rifle that screwed up
if he'd have said "Well let me think about it" and walked outside with the rifle, no doubt OP would have hit the parking lot and they could have determined if he would have paid more.
just bad circumstances.
If the owner was apprised of the full story and still feels the OP was persona non grata, I'd be happy to comply were I in his shoes.
if it was accurately depicted then imo the OP did nada wrong, just the seller
loose lips, sink ships