Haggling is a fine art. Over do it, by even a tiny bit, and you usually queer the whole deal. I'm guessing that somewhere along the way you missed some signs he gave you that went from "This is a win, win deal." to "I'm giving him a good deal." to "He's just being greedy.". Next time spend way more time talking about how wonderful the stuff you're giving up is and less time talking about what he's giving you.