>>>One of my favorite potential ( a potential I never fulfilled ) client from hell was the Dr. who wanted me to write a medical app and said " I could do it myself but I just don't have the time."
>>>
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>>I have been told that by two different clients. I was smart enough to keep my mouth shut.
>
>I wasn't. As Whil used to always say - Better to pass on a client and be sorry than take a client and be sorry.

I think there are at least a couple of criteria you can use to evaluate potential clients e.g. attitude and technical knowledge:

1. Good attitude, knowledgeable: great client
2. Good attitude, ignorant: needs work but can be great
3. Bad attitude, ignorant: client from hell
4. Bad attitude, knowledgeable: ULTIMATE client from hell

Sticking with a client who has a bad attitude is like those women who stay with men who beat them - they have a misguided notion that if they just try a little harder, they'll come round...