Suppose I want to exchange Bitcoin to other USD, as like neteller/skrill. Then how can I trust someone on online?
It can be fraud and I can lost my bitcoin. is there any trusted source/exchanger?
How can I understood he is Trusted/reliable?
Simple solution to this issue is using an Escrow service. Many members are offering such services here as well but go with a reputed member. Also, check out the trust of the member offering that service and choose one with at least 50+ positive trust. You will have to give him some fee to manage this.