Unfortunately the restaurants have you over a barrel because you can't see what they do to the food when you send it back. If I do complain and I am suspicious about the result, I head to websites such as Urbanspoon to review the restaurant. I once left half my meal on the plate at a pub because it was tasteless, and the chef came out to see what was wrong with it. He offered to give me anything else on the menu to replace it. Needless to say we continued to return to that pub for years. The good ones will be around for a long time. The bad ones go out of business.