Plank...... If it was faulty or not as you described, then fair enough. Offer to take it back off him minus a fee for the fucking about? But in essence you are quite right, if he couldn't see it was for an external wastegate, and that it was unused, then he shouldn't be buying it!!!

And it WILL fit his car, just needs the correct turbo and wastegate! Out of interest how much did you sell it for?