Generally I find the only reason someone should trust a critic is if an individual one shows that their tastes constantly line up with yours. Even with something like rotten tomatoes I always take it with a grain of salt, assuming it's working properly it's still only a general censuses. Typically if something is like 96% I can usually assume it's at the very least decent, but that doesn't always mean amazing or if it's at 0% you can usually assume it's terrible but otherwise I've seen movies all over in between that I've found myself having different opinions from the general consensus. I find it's best when a critic really goes into details and describes what he likes or dislikes about a movie, so that I can judge myself how I might feel about it.

Frankly I'm more likely to trust a friend that I feel has good tastes opinion on a movie/game/show over anything I read online good or bad.