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.
Survey Junkie uses a point system for their rewards. For every survey you complete, you’ll get anywhere from 50 – 450 points. 100 points equals $1. Unlike some of the other competition, Survey Junkie is very honest about how much you’ll make. They clearly say on their website, “You Will Not Get Rich” taking surveys. This is refreshing to see after so many websites claim you’ll be able to quit your day job and sit at home taking surveys all day.