Though I have no experience in any Bitcoin related services yet, I think the reason why people put trust in a service generally is its popularity among its users. I first check feedback, reactions, and experiences of other people related to the service that's why it is a plus point for me. Another is that if it is recognized by reputable people or company in that field, another plus point. But most importantly, you must do your own in-depth research and investigation so that in the end, you won't be scammed or you will gain a good advantage with it.