I'm no expert on ethics, but I wouldn't think that you'd be obligated to cut him in on the deal. If he was happy with the deal because he didn't want to mess with eBay, then so be it. If you can't have a clear conscience about it for some reason, then maybe get him a nice pair of baseball tickets or a gift certificate to a nice restaurant or something like that. I dunno, I'm just brainstorming here - I've never been in a similar situation.