Sorry to sound picky but the first part of your posting is at odds with the end.
If a customer is a pain, or the job is under priced, then just give it go at raising the price.
See what happens first before pre empting the outcome. If nothing else, the experience and discomfort of asking for more and then walking away if it is a 'no' will help in terms of posture for the future.
Posture will get better priced jobs in the long run than any amount of know how.
If they agree to an increase in price, then it's a bonus, if they won't pay for whatever reason, forget anybody else, search for new jobs and do what ever it takes to get them be it spending days leafleting or time door knocking.
Cheers