I used to do the same. I don't any more. After being thrown under the bus for doing EXACTLY what the customer said, against my recommendations(documented no less), no thank you.
WHICH happens to be a great way to make your point even stronger. Telling a customer "no, I won't" gets them to think, perhaps a little. I've had a couple people ask me why I won't, and basically say, "When the shit hits the fan, I don't want to be involved, don't want to clean the mess up, and don't want to take the fall for anyone but me".
I now use a phrase that sums up everything perfectly. "Good IT is expensive, bad IT is costly".