This. I probably buy about 1000 stacks of elementium ore a month from the AH, rarely at over 20g. They're definitely coming from botters, likely on hacked accounts.

A good way to learn the botters on your server is to head to Uldum and camp a spot around the rim, preferably a rich elementium or Pyrite node. Just sit there, and watch for typical 'bot' behavior:

-Using a minimum-speed flying mount
-Erattic Flight pattern
-No Response to Whispers (try to have an alternate-faction friend in real-id to help with this part)
-Minimum Gear/level for the zone

Learn these botters, put them on a list, and then check that list against the AH. It's pretty easy to avoid buying from the wrong types this way.

In addition, find someone who does their own farming, and get them as your supplier. Establish a base rate, and give them a bonus every fourth delivery or so. Try to find somebody for each gathering profession you have, and share them around your guild. The more business the supplier gets, the more likely they'll join up with you, giving the guild an in-house supplier.

When I used Auctioneer I could usually tell the botters/hackers. They would sell a lot of stacks at the same price with a name like Kgthrfsnl. Since then I switched to Auctionator, which does not give the name of the seller, or if all the stacks are from the same seller, and I find that I no longer ask myself if the seller appears shady.

This article makes me want to quit selling Vial of the Sands.