Another forum I frequent has something setup that makes trading much safer, and easier.
Under everyone's user name they have two sets of stars 1 to 5 (Mushrooms, actually, but thats another story). One for general ratings, and another for trades. When a person leaves a rating of 1 to 5, it affects the bar displayed under the person's name and averages out. The administration treats the trade ratings very seriously there, and leaving falsified trade rates can result in being banned.
When you click on each bar of stars under a persons username, a corresponding page comes up with comments from each person who left the rating; Describing the reason. For general ratings it might be something like "Nice post! Very informative" and for a trade, it would describe their proficiency in holding up their end of the deal.. i.e. "I bought an LCD off of (username) and item arrived in good condition, as described.. but it took a really long time to arrive." to give people a quick and easy way to gauge if a seller is trustworthy or not and meets their expectations in trading.
The classifieds are a very very active forum here, and something like this would benefit all users, and make it much safer environment to do trading. :)
I realize it detracts from mp3car.com sales, so this probably won't be implemented.. but I figured I'd toss out the idea anyways. :P