For the most part, all the players that say they are new are actually pretty decent players. Once you explain to them the mechanics, they usually get it down in one pull(maybe they mess up once if its something kinda unique/challenging).

I don't mind someone saying they're new to a dungeon, but obviously once you get to a certain point there are basics you should have down pat. For example a level 50+ tank should know how to position mobs away from a group, know when to pop CDs, etc.