I would live by the same thought, if I break it I buy it. I wonder if it had a 'mirror bore'. There was a discussion here not long ago. I wonder if the borrower could just say that there was a partial obstruction in one barrel, and then a 'pressure wave' caused the bulge in the other barrel. Sometimes, it doesn't seem to wash.
If the seller loaned it out to two people, and the seller is an expert, then the gun came back to the seller in proper condition after the first loan out came back. But, the seller didn't spot the problem until later.
I know what I would be thinking if I thought I shot the gun in a responsible way, and I got a heated call later. Unless the seller could narrow things down enough to play the fault card, they might possibly consider themselves lucky that it didn't let go.
