Should upgrading on a site to be paid be a scam?

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I think there are 2 ways to look at it. If you join a site knowing you have to upgrade to be paid then the site shouldn't be thought of as a scam. But a site that has been paying free members and suddenly decides only to pay upgraded members, then I think that is scammish. Paid to Click sites are the worst because you're only getting a cent per click, by the time you do reach cashout, it is going to be gobbled up by having to upgrade. So what are your experiences? Should we label these sites as scams?