You can set auctioneer to undercut the bid as well, or to have the bid as a percentage of your buyout.

For the most part, it works by setting maximum percentages of the average price in which you will undercut (or overprice your auctions if you're the only one selling stuff).
You can configure it to go with your historical (overall) data, the last 3, 5, or 7 days of scans etc.

You have the option for fixed price auctions as well.

Appraiser is the part of Auctioneer which handles mass listings.
It gets you all the standard options, such as number of stacks (or all), stack size, only list 'x' stacks, duration etc.
You can hit refresh for any given item, to see each person who is listing the item.
You can hide the item from Appraiser so you don't accidently bulk list it.
You can check to add it to the items you bulk list.
There's a button for bulk listings, if you alt click it, it will refresh all of your batch post (checked) items.
If you alt + ctrl + shift click it, it lists all of your batch checked items.

Some things like rare recipes, I always sell at a fixed price.
My assorted toons purchase them for 35 silver or whatever.
And then mail them to my auction toon for the faction (or to my neutral AH transfer toon, for recipes the other faction cannot get).
And then the auction toon will list at a fixed price, with the "only list 1 of this item" checked.

Most things, I want to refresh the view to see what others are selling for, and to undercut them by 1 copper.

One of the better selling items, is alliance faction specific (unlimited quantity) vendor pets, like the kittens, rabbits and moth eggs.
They cost between 30 and 50 silver each.
And sell for 7-15 gold each on the horde side.
I make in the neighborhood of 500g a week doing this.
Interestingly enough, the horde pets sell for crap on the alliance side as there are so many people undercutting constantly; you're lucky to make a 50s profit on a pet which cost you 50s to buy.