See if he will take sexual favor's as payment ;) I'm not sure from a legal point of view, but I'm sure they can't just do the work and bill you for it. I know my mate always rings people up to let them know if there is anything else, but will say he can get round it if it goes bang they took the risk and not him. So I would just say stress that's it you can pay cash maybe if that's maybe how he's going to doit ?