Some of it is gut feel. If a person's first impression on me is that they're a douchebag, they get an instant "thanks but no thanks".

But there are some more concrete clues. If they ask for bulk discounts on hours, if they ask to negotiate the rate up front, if they seem to talk "bigger" than they need to, if they think the work you do is "easy", if they act like they're doing you a favor by offering you a chance to bid on the business, etc., those are hints that money will be an issue or that they don't really value your services.

I never, ever, deal with small local businesses - i.e., those that don't seem to have owners with corporate backgrounds. Smaller business owners tend to not be accustomed to throwing around >$100/h for services. I'm generalizing, but if they're paying their staff $10/h, they expect 10 times the output for $100/h. IMO, those guys are trouble, run, run, run away if you can, because you'll get nickeled and dimed out the wazoo.