I haven't check out this market that people are talking about, but in other games, to put items up for sell you have to put up a fee. In Champions Online, you pay 5% of the selling price, your auction last for 5 days. Ex: you selling a sword for 20k, you pay up front 1k, then your sword in the auction house will last for 5 days. By the end of 5 days if nobody buys, your sword will be return via mail.
This will stop people from putting rocks and crap for 200k gold and there will be some idiot who buy it by mistake.
And we don't want to look through an endless list of outlandish offers. This way we only see mostly acceptable offers.
It will also be a great money sink.