How do you deal with clients with bad taste?

There is no such thing as having bad test. Everyone has their own tastes. You are being paid to provide a service and so as much aesthetics are concerned you really have no real control or input about it. Clients are always right. All you can do is inform the client why such and such design choices are wrong. If the client still refuses to change his /her mind just do has told. Sometimes you both can make an agreement on something that works for the both of you.

In the end what is more important to you? Making money and being a professional that can follow instructions yet still provide satisfaction to more and more clients or a professional that argues with each and every client on design choices that are not aesthetically pleasing to you personally?