Hi Black Hand: No I think Dumbledore trusted Snape because of something important such as Snape giving him one of Voldemort's Horcruxes OR giving Lily some potion to protect her baby from Voldemort OR taking an unbreakable vow to protect Harry from death, even at the cost of Snape's own life. Dumbledore trusted Snape because something HUGE and UNQUESTIONABLE passed between them. But what?