Taking paid surveys can become a well paying job if you work hard enough at it but you won’t start bring in buckets of money right from the start. But don’t let that demotivate you to start taking paid surveys. In the beginning you don’t have control over the survey offers you receive, but if you keep at it then after some time your per-survey-rate will go up as you become a more reliable source for paid survey companies. Then you’ll be surprised how much extra money you can make without putting in very much effort at all.
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.
It’s a very well-known scam. You cash the check, then they ask you to either wire some of that money back to them as some sort of fee or buy something for them and send the item to them. So, you deposit the check, then wire some cash to them thinking that the check you just deposited will cover that. A few days later, after you already send them the money, the check will bounce and the money you send to them will come out of your own account.