The Auction House takes all the skill element out of the game on normal mode. Anybody even moderately interested in playing the game with a bit of risk (which also implies you are playing hard-core-die-once-and-your-character-is-dead) - avoids the Auction House like the plague when playing Normal Level.

I understand the Auction House is essential to completing the game on Inferno level, but good players can complete on Nightmare without using it. I don't know about Hell level - that's probably where there is a judgement call required.