I'm going to show you something.
What in that image stands out? What, when people look at it, immediately jumps out at them first?
In fact it's so visually strong that people don't even need to know what 18.7 is a measurement of, they'll just know it's a little better than 17 but not quite so good as 20.
Remember the first part of Blizzard's mantra is Easy to Play. This is stats made simple. How good is that sword? It's 18.7. That's all most people will feel they need to know.
If that weren't already strong enough have a look at the AH interface. What does it sort on by default? DPS
Item, DPS, Bid, Buyout, Time Left. The game is structured as if there's only one thing you need to know about a weapon - DPS.
In fact there can be other dps elements to a weapon that don't show up in the number. An 18.7 dps weapon with bonuses to crit strike chance, crit damage rating, and Strength might be a much better dps option than a plainer 20 dps weapon but most players would never know. Your buyers generally won't know.
Shopping is all about taking mental shortcuts.
Harvard Prof Robert Cialdini told a story in his excellent book Influence
about a woman acquaintance who was selling gems. She left a note for an
assistant to half the price of a slow selling stock of Jade. He
mis-read the note and doubled the price. Suddenly these gems that no one
wanted sold out. She asked Cialdini why?
Most people have no clue about what makes a good piece of jade. Actually
we have no clue about lots of things but our brains have evolved a
mechanism to cope. What we do is we take mental shortcuts. In the case
of jade we look at the price.
Jewelry is a very personal present. We tend to buy it for someone close
to us - a wife, a daughter, a mother. A $25 piece of jade is a bit too
cheap for most people to buy as a present. A $50 piece of jade is just
right. It doesn't matter that it's the same piece of jade in both cases,
we equate quality with price, It's a method that works 99% of the time.
Part of mastering the Auction House in Diablo 3 will be understanding the difference between buyer psychology and optimisation.
Next consider movement speed. Now arguably for certain fights, dangerous act bosses, Inferno and so on it might make more sense to have combat stats on your boots than run speed. But no one playing Diablo will want to move like they're walking though treacle. It's too mentally offputting to consider. So boots without movement speed will almost certainly be underpriced relative to their mods and boots with movement speed, especially max move speed, will be expensive.
There are six principles in Influence that explain why people make decisions, particularly decisions where someone else has talked them into something.
Reciprocity. So if I play with someone and give them a nice item they are very likely to respond, especially if there's a sustained social relationship. This of course can be manipulated, one could give people rare boots with no run speed and be quite likely to get random rares back.
Commitment and consistency. If we set up a Sunday afternoon gear swap market then over time people will come to really appreciate it. Sticking to the same time every week and never missing a week could establish some sort of player trade fair.
Social Proof. People will gear up in the way they see other people developing their characters. If some people in Inferno early on get a very distinctive look, the item that gives that look will be sought even if the stats aren't great.
Authority. Check what top players and D3 celebrities like Force and Athene are wearing. Buyers will want to buy the same gear. They know it works. The exception, sadly is me, because I'm expert in specialising in random junk ghetto gear and still kicking butt. Maybe, come release, if I attract a group of fans who particularly want to emulate me we'll see a trend for blues with + Gold Radius on. A boy can dream.
Liking. People are influenced by people they like. Force will probably get copied much more than Athene because Force is more likeable. Athene's rather odd sense of humour puts many people off. So expect people to influence and be influenced by friends and guildies. If you sell to someone ask them if they are in a guild and if anyone else in the guild would like the item. Being introduced by someone they like makes people more receptive to you.
Scarcity. People often panic buy when they fear a window of opportunity is closing. When you trade you can excite a buyer by mentioning that you have to go soon or that someone else is interested in the item. Of course scarcity is already heavily built into the item system so people will be open to the notion that your offer is a unique and special chance to enhance their character that they'll regret missing if they don't buy now.
Good luck in the D3 Trade Wars. I think the getting rich game is going to be as fascinating as the RPG!