Several posters have flat out said that you automatically should trust the DM. I asked above if that trust was a two way street.
DM's need to trust that their players aren't out to make their lives hell, unless proven otherwise.
DM's need to trust that their players use the character approved, unless proven otherwise.
DM's should trust players to be rollling relatively fair dice, unless there's good reason to suspect otherwise.
Players should trust that the rest of the group are being reasonable in their approach to rules.
Players should trust that the DM is trying to be fair.
Players should be able to trust that no other player is there just to spoil their fun.
DM's need to try to be fair, unbiased, and run an amusing game, for whatever value of Amusing is acceptable to everyone in the group.
Players should realize that DM's can't always be fair, consistent, and amusing all at the same time, and that if rules mistakes are made, they are either unintentional or are for specific effects.
So, yeah, the whole trust is a two way, not entirely balanced, street.