Learning when and how to convince a client their requests are stupid is a skill that comes with experience.

Sometimes it is possible to ignore or "misunderstand" a request that is not in your client's best interests. If they were really committed to their bad idea, you'll hear about it again. !This only works if you haven't already tried to convince them it's a bad idea!

And some clients you just have to suck it up. "It's their money," is a mantra I repeat to myself when I get frustrated.