Well the problem was the casual player generally never learned how to MF. They would just save any rare or unique item thinking its really good and they could trade not know its junk that no one wants.

If everyone knew to level a character up to 85 and continually kill certain bosses over and over again then there would be plenty of good items that they can trade for other items they haven't found that they need.

The even bigger problem is that eventually a curency would develop, be it SoJ's, 3/20/20's, HR's, etc.. people who have them only want to trade them for certain items. It makes it really hard to trade good items (that people use), but just weren't valuable enough to be worth whatever the given currency is. And if the currency was duped enough like SoJ's were back in the day, you were trading 30-40 of them for an item.

Gold should solve this problem though. It will take away from the barteringness (to make up a word) of trading, but I for one have always dreaded trading with anything but the going currency since its such a pain to deal with some people.