I read a gold makin post somewhere about how undercutting is almost always best and how the poster always posted his epic gems while online, then cancelled his auctions before logging off for the night. He stated this saved him money in listing fees and saved him logging in to a bunch of unsold auctions that were undercut anyways.
I must say that this is the stupidest thing I have ever heard. I am online for 4-12 hours at a time and I must say that over 90% of my sales come from times when I am not logged in. More Specifically, the wee hours of the night as the Australians and overnighters tend to buy the vast majority of my items, probably since there are a limited number of crafters on at those times. I also can testify that while enchanting for tips overnight in the late hours, my business has next to no competition.
So don't forgot about the overnight market on your server. Often times you can list your items at regular values instead of undercutting, and if placed right in the list of items for sale, they will still sell, since the cheaper ones will be bought out and your items will then be the cheapest when that Aussie player logs on and goes to purchase.
So think outside the box. If something sells, ask yourself why did it sell and how you could have made more profit off that item.