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.
You are right, Website's that are scamming people are really out there so it is better to ask for professional people who already invested on different sites if they did not get any problem before investing on a specific cryptocurrency exchanger or holder.