A very valuable lesson learned.

When you buy something, or sell something, over the internet, realize that it is not the same as an in person transaction.
1. if you are the seller, insist that if the item is going to be returned it comes back in the same condition as it went out (and make sure you can document the condition), and also make sure that the buyer will pay for the return.
2. If you are the buyer, make sure that there is an inspection period, and make sure you are prepared to pay for the return shipping, if necessary.

No gun is worth the bad blood that this transaction caused.