This happened to me once. I still buy from the guy. He always references it in embarrassment. Didn't phase me.
Count this guy as one of the good ones, save him as a fav seller, and look at his inventory in a positive light knowing he deals honestly. And keep the coin unless you truly prefer the other based off the pics.
I always remind myself to remember the human side of things. Mistakes happen. IMO, from what I can tell from the [edited] posts, you handled the situation with grace. I save the negative feedback for the true cons, to warn others. Otherwise, I give people the benefit of the doubt; we all have bad days. Also, keeping in mind that many times a seller may not be pleased with the transaction because of a low-ball bid; and that reflects in their interaction. When I list something of value for only $.99 and then it sells for that, I have only myself to blame for taking that risk, and try to be gracious to the bidder. Kindness does spread, but rudeness is infectious.