In my case, I dont really have to "trust" a reviewer, because I dont watch reviews of games I want to play.
I do look at reviews after completing games though, as I always find it interesting to see if my opinion is shared by others.
When I do, I tend to see if Yahtzee has reviewed the game in question, as he often brings out similar bad points about the game that I might notice, or when he says something which is terrible about a game, I will be like, "Yeah, what he is pointing out actually WAS annoying now that I consider it."
I also have a look at IGN or Gamespot, just to get a review where they usually highlight the positives of the game, just to get both ends of the scale.
Finally I check out Metacritic's user ratings, but only the reviews which graded the game as mediocre. The lowest grades tend to be "OMGZ This game suxxors!", and the highest grades often tend to be "This game is the most awesome game ever seen, go buy it now!" If you read the mediocre reviews you tend to get some pretty well rounded reviews, where both highs and lows are highlighted.
I think this gives me a pretty thorough general feeling of how others find the game to be.