I would recommend him to one of the more "commercial" board makers that is out there if you really don't want to make him another board.
In small business, we face this all the time. There is a theory of rating the customer, ABCD. Even though you treat every one the same initially, you try to nurcher the AB, C is a price shopper, and D, you will spend more time and money to satisfy them, but you will probably lose in the end. Hey, this is a small business. If it is a large business, you can pay someone to deal with a D person. Obviously, this person is a D from all indications. The MO of these customers are they are the "perfect demanding" types, where they can do no wrong and no one can tell them that they are wrong, because the are "perfect". There is a potential this person cannot be satisfied, where he thinks he holds no responsiblity in any of his actions, and it must be the product's fault. If you think this guy is that type of a person, you will probably have to to deal with this sooner or later once you sell him a product.
If you want to make him a board, because money is money, one thing to do, is be up front. Say, hey, what happened in the past was not fair to me as a craftsman and businessman. You blamed poor craftsmanship for things that you did, and spread that all over the interweb. As a craftsman and a businessman, how will I be assured that something like that won't happen again? I am a craftsman, and I stand by my work. If there are any defects, they must be legitimate......
You get the idea. If communications are established initially and the ground rules work out, hey, take his money and make him a board.