Yeah I agree this guy is no friend. What a richard. He is going to blow you out of $20 because he was too broke and lazy to get it himself. If I were you, I'd do what Wedge suggested and trick him into deleting it.
Say you are going to setup a TDM and tell him you need to install an add-on and tweak some settings for it to work, then just remove the key. He can hardly complain, it isn't his.