That brings me to an email I received today. Sevil mentioned that he was recently contacted by an in game mail about setting a common price for the Netherweave Bags in the AH. In the email, they mentioned he is thinking that in game mail was sent to everyone competing in that market. First off, you want to respond "in person". Send a response saying it would be easier to talk in game, to holler when you are on, but that you are interested in doing this (whether you are or not, you need to feel them out). Then toss him on your friends list. If they log on, shoot a quick /tell to them. Read through the post first before doing so to get your bearings on who or what this guy is...
A few things to think about in this situation:
1. One of the issues with Netherweave Bags is that folks were "told" to stockpile them for the Cata expansion. My first guess is that you have quite a bit of competition (most servers you have 4-5 on average selling them), as there are others that stockpiled as well, so unless you know who has what amount, it would be tough to win at this game and "own" the market. With that said, let's next it....
2. You need to buy out EVERYTHING for these bags. The cloth, the bolts. You need to set a price point on what you will pay (and you mentioned this in your email to me, so that's a good thing) so it's not profitable for anyone else to enter the market. When I do this style of bullying folks out, I buy so the profit is only a few gold for the other folks (given I have a good stock already). Either you stick your toes in the water, or dive in. I prefer to dive....
3. Offer to buy him out. Now this might not happen, but for someone to contact you, they are pissed off about the whole situation. Once again, I have done this style as well. Tell them:
"Instead of undercutting each other to death, lemme buy up your stock. I know that they cost 5g to make, so I will offer you 10g each (or less, your deal, right?) for all you got in stock". Believe me, alot of folks go for this in quite a few markets....
4. Since we have no idea to see who has been selling what for how long.....wait. We kinda do. This is where the Undermine Journal comes into play. Search your server, and I want you to click on your competitor's name, and check their markets (just an example here of what you will see)
Now you didn't list whether you were H or A, but I just picked one that was selling for reference. When looking at my market, I speculate. Now 85% of the time I seem to be 62% right =). Lemme tell you what I think when I see this:
I see that this seller's "niche" market is the bags (only three "items" posted in 2 days)
I see that no one has undercut the bags in 9 hours, so they are not an "AH" camper competing
I see that your server is dumping the Darksky Treads...4 undercuts in 8 hours? hmmm....
Now let's check your mats quick on the bags (i.e click on the Netherweave Bags):
Currently, there is a 15ish gold markup on these bags, and reading the sales, they sell consistently throughout each day.
*You always want to check your mats prices when getting into any market, and once in, lock the door. Don't let anyone else in...
We see here that there is a consistent sales platform, and that the demand is there to be a very lucrative business, given the 15g profit (selling a few a day will add up over time). Basically, as long as you have some on the market, you will get sales sooner or later.
*When posting these bags, I would post in 12hr, 24h, and a few at 48h just to make sure that I never do NOT have any on the AH. Before I hear hate on this, see my point. If you don't have any on the AH, you have zero % chance to sell. If you keep the AH constantly supplied, you don't have to worry about the 0%, you at least have a fighting chance to get sales.
Now I hoped this gave you an idea on how to not only work with a "price fixer" but also checking the "resume" of your competiton. This will obviously work with many markets, not just the bags. So when you are competing with someone, do your homework, and know who you are competing with, that's a surefire path to winning.