Just some advice for new authors:
I would recommend giving possible proofers/editors/critiquers a sample of your work, usually only one chapter and judging to pay them based on a returned sample.
I have screened three paid Beta Readers this way and it has worked out great! I would also recommend websites like oDesk.com and freelancer.com. These sites usually have ways of forcing refunds if the project calls for it. Also, they have fixed-price projects where you do not pay a dime until the project is completed, and you both agree that the finished work is complete/adequate.