Stack size, that is.
This post is dedicated to all of the industrious goblins out there who listed 217 of any item, in stacks of one.
Please go die.
On behalf of every goblin out there, I would like to thank all the players who list your stacks in reasonable numbers. 5, 10, 20, 200. You make our day. If you list large quantities of things in stacks of one, you are only hurting your own sales. Now on certain markets it's fine to list a reasonable quantity of items in stacks of 1. Darkmoon cards, fortune cookies, even dust/essences.
However, if you list more than 30 auctions, you're not going to sell as many. List 10 in stacks of 1, and then put a stack of 20 up! Not only is it less work for you to open the mail, but that stack of 20 is a lot more appealing to anyone who needs more than 1 item!
If I'm posting a dumb amount of something, I like to post in a ton of different stack sizes. I'll post a handful at 1, 6-8 in stacks of 2, and so on for stacks of 1, 2, 3, 4, 5, 6, 8, 10, 12, 15, and 20. It's a bunch of work to vary it so much, but guess what? They always sell.
And after all, isn't it all about making sales? At least that's what my boss tells me every day. =)