Basically we don't know the risk in every site if you invest money in a site first is you don't know if the site was trusted there are site that can give you small profit but many site are just scamming people who invested.
About scamming. I am joining in signature campaign. A bounty signature campaign mostly i am joining. It is too risky to join and to earn there because theres a possibility that the campaign is not going to be successful. Actually i joined one signature campaign that is not successful my efforts and time is wasted. But its okay because i am ready for that.