There are legitimate ptc sites...you may read forums that say which is legit and which is not, but for me the best way to see is by testing these websites by yourself...if they pay once you reach the minimum amount you cashout, then it's legit...if it doesn't then it's a scam.
There are some ptc sites that I have proven to be legit: Ojooo, Clixsense, Neobux and Paidverts.
Scam: Quickbux, Exchangebux
I have earned a total of $25 from clicking on Quickbux and Exchangebux, but they have never sent me my payments. Have checked every now and then if my payment method is updated, but still haven't received my requested cashout. I've also submitted a complaint ticket, they didn't reply at all and even closed my generated ticket. Don't waste your time on these sites.