How to know which sites are scams and which are not?

Check out ptctalk.com , and find out which of the GPT sites out there are scams and which are legit. They also provide you with tips on how to earn more and how to decide which sites are scams. They have a list of sites that have payment proofs for you to see, and much more things that are helpful as well. This is one of the sites i used to get to know all about PTCs and how i found out which ones to join and which ones not to. ; )