Well there is many obvious signs of the scam sites, for example they ask for money without offering real service , or they haven't real local or exact address or phone number
You can find many site like this on deep web.I totally shock on how much the deepweb is change for now.There are many link in hidden wiki about totally scamming service that only rob our money.For example the most stupid but many people fall for it is btc doubler.Just think logic how can they double our bitcoin in short of time ? At here we already know that this site is totally scamming.