As a consultant, you know that methods that work in one circumstance don't always work in others. Your clients were probably high profile and dependent on reputation. You wouldn't recommend the same "pick your price" reimbursement mechanism to them if they sold something over the net to anonymous people that can be endlessly and easily copied like software, porno or high resolution images. As a good consultant, you know better than to universally misapply mechanisms that only work in specific circumstances.
Unless they are crooks. Then you had better be prepared to protect yourself and maybe even sue for damages and restitution.
Tell you what. Leave your garage door open. Word on the street is that Vinnie the Customer like your wheels. He'll be by to hotwire and borrow it for a couple months or years. Oh, he could afford to buy his own, but he doesn't want to spend his money when there are great folks such as yourself who have already spent the money who are willing to share.
It's a good thing there are people like you in the world who aren't uptight about personal property rights.