You probably would've been better off saying nothing at all than you are now that you asked for an undamaged. Now he's going to use it as a way to get some extra money.
The way you phrased the post makes it sound like every coin was sold, but he happened to have one or two extra that he didn't list in the auction and he realized he could make a few bucks by selling a coin off-site, thereby dodging eBay/PayPal fees. Run, don't walk if the seller is trying to get you to deal with him outside of eBay. You're not covered by eBay's buyer protection if you deal off-site. And if eBay finds out they will ban you.