Obviously you didn’t sign any papers. So if you had any obligation to him it would be a moral one. But I’d say you don’t have any obligation to him, not even a moral one. Buying a house is a gigantic financial transaction, and if you think his bad attitude (or other shortcomings) would get in the way of representing you as well as possible and cost you money (and I’d say there’s a good chance they would), then find somebody else.
Sure, he showed you a house. But you didn’t know then that he had a bad attitude. Now you know that. So if he asks you why you went with somebody else (which he may), then just tell him the truth.
