Are the various "Paid on click" sites authentic?

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Hello everyone! I was just wondering,are those numerous sites which you find in the internet that promises to pay due to reading mails or their advertisement,once you reach their minimum payout,really authentic and does keeps their promises ? Or, are those just some other form of internet scams? WHat do you people think, if someone has lots of scope to do them,should they go for it? Please advice,as I am a bit confused with all those offeres and so on/