Any relationship you form needs to be based around the idea of 'good will'. Respect needs to be mutual, and the desire to find amicable solutions also needs to be mutually held.

I think it's usually quite easy to tell whether a client is going to be bad news; e.g. if a prospective client is looking for the cheapest solution above all other requirements, or they're very vague about deliverables it's probably worth giving them a wide berth.