Paid Surveys

They include sites that seem to be their competitors because they earn referral fees when you buy memberships. A couple mentioned in scam forums even try to dupe you into buying the same list at other membership sites they own under different names. Naturally, these sites also have an incentive to exaggerate how much you'll earn from online paid surveys.

The concept of data mining and profiting off that data mining isn't anything new.  And while some companies engage in some rather disreputable practices to do this, Global Test Market seems to be doing just fine with the whole “consent to disclose” thing.  More importantly, in some cases this may help you as some companies will offer to do more specialized product testing once they've identified you as their target demographic.
You're unlikely to "get rich quick" by taking paid online surveys. You will, however, likely earn or win some extra spending money, or free or discounted goods or services. Doing paid online surveys can be seen as a way to get a fairly steady flow of a decent amount of cash coming in each month. If you enjoy participating in online surveys (especially if you enjoy sharing your opinion for prizes, coupons, and other more typical non-monetary earnings), then paid online surveys is a good choice for you.
IOCS is a not-for-profit research organization that conducts studies and experiments on shopping-related behavior – things like how we, as consumers, evaluate products, how we make the buying decisions, etc. Although the focus is mostly on shopping related behavior, some of their experiments and studies include broader areas of marketing, psychology, and economics.