The sellers last message makes him come off as neither fair or reasonable so just wanted a few opinions before I draw a line in the sand simply because he's a douche bag!

I'm assuming you meant "buyer" and not seller? You're the seller in this, right?

I think that most buyers do not realize that when they cancel a sale it costs the seller money.
I haven't sold on ebay but from reading the replies to this it seems that ebay is very generous to refund your transaction costs. That's not the way it works in regular retail.

When I had a retail business it never occurred to my customers that when they got a refund it cost me several percent in credit card fees coming in going. The credit card company charges a percentage for the sale and a percentage for the refund. (I've been retired for awhile, thank god, so I don't know what the current processing charges are)

So the buyer may have been quite innocent (and not douchy) in asking for the refund thinking it was just a few clicks and a few minutes and had no idea that costs may have been incurred to you.

PS: I am NOT the buyer in question. And I accidentally buy duplicates all the time and won't cancel and order just because I screwed up. I figure it will be a good trader at some point.