Don't wait to get email from them about surveys. It rarely ever happens. Check the boards frequently. Studies close very quickly. Some pay, some do drawings for Amazon GC's. The odds of winning are much better than at regular survey sites as these studies accept Far Fewer Applicants. When you log in to check surveys, ignore where it says "Credit." The reward is explained after you enter each study. They are trustworthy and reliable.
https://cgi.stanford.edu/group/gsb-behlab/cgi-bin/behlab/registration/fp.cgi
Compensation: Researchers compensate individuals who participate in their studies by gift certificates to Amazon.com. In general, studies pay between $5 and $15 depending on the length of the study. In addition to paying studies, participants can also take part in non-paying drawing studies, in which their participation enters them into a drawing for one or two larger Amazon.com gift certificates.