How do you tell which one is scam?

Hard to tell. So, what I usually do is to give it a try for some time without making any commitments or payments if they ask for it. Let them meet their commitments first !

It can be pretty tricky sometimes to know whether a site can be trusted or not. Any time a site requires you to pay just to become a basic member, then I just assume that it is a scam. Also, sites that promise to make you tons of money don't seem very legitimate to me either. I tend to trust sites that only promise smaller amounts of money, because I feel like they are probably more honest. Also, if there is a particular site that I am interested in possibly joining, I often come to mylot and do a search here to see if there are any discussions about the site first. That way, I can see what other people have to say about the site and if it can be trusted. If there are lots of good comments about it, then I will probably join it, but if people have said a lot of negative things about it, then I stay away. Good luck!