To know that a service such as an online and anonymous bitcoin transaction is legitimate, one must sacrifice whether he sends first or he receives first. Here in forum, you'll find a lot of trusted users whom had already been transacted with other forum users hence gaining a trust tag, in which is a helpful tool to provide other users whom to be trusted and whom are not. Yet if some stranger approached you for a transaction, better not invest nor initiate first. If he should be trusted, he sends first.