Also be ready for Ebay to side with him. Unless he is overcharging for shipping, they aren't likely to step in and force the issue. More than likely they will just say that US postal rates apply and if the rate is what he is trying to get now, then you probably won't get any satisfaction. Just speaking from experience. The only downside is that he might be able to complain about you and leave negative feedback. Depends on how much he wants to play this out.
True, Ebay's rules are the rules of a game. In some games, luck is on your side, and in some no. One thing I know for sure is that the feedback rules have changed over time: the seller is no longer able to leave negative feedback. Correct me if I'm wrong, but I remember that this change dates from a about two years ago.