I know it's hard but some people just won't listen and the best you can do (indeed your professional ethics require you to do) is offer the best possible advice and the reasons why an alternative won't work. At the end of the day, it's the customer's money. I wouldn't worry about your name being on crap because of your other work and reputation. But, if you really feel that the result is too awful to be associated with your name, then don't take on the job for your own sake. I say that in all honesty -- you have to be able to live with something with your name on it.