Find out if a site is a scam by using a few different sites. Taking two mins to search on these sites before joining any site where you think you can make money will save you time, money and headaches.
scam.com - No sign-up required. Huge forum, been around for many year. Goto "search" and enter in the website w/out the www in front. Enter in the lil passcode (don't worry it's not case sensitive) and click search. You will likely get a few results from other users sharing positive or negative experinces and sometimes payment proof if it's a good site.
gptboycott.com - Again same thing, no sign up required, click "search" enter passcode and get results.
(clicking links takes you directly to search feature)
Using these two sites and 5mins before joining ANY site will save you money and time.
Survey Police - Specific for surveys, find out which ones pay, which ones don't.