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.
You can expect to earn $2-$5 for most of the surveys in general. For some special surveys you can earn up to $50 per survey but those are rare. Harris Poll also conducts paid focus group studies where you can earn $50-$100 per study. Usually these focus group studies are 1-2 hours long where you interact with other participants under a supervision of a focus group moderator.
Joining isn’t as straightforward as merely signing up, because you need an invite. However it’s not as tough as it sounds, as there are plenty of links doing the rounds online if you look hard enough, and Pinecone also advertises on websites, so you might get lucky by keeping an eye on banner adverts. Once you’ve signed up, you’ll be vetted to see if you qualify – based on whatever demographics their clients want at that point – and if so, the fun begins!
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.