How does auction house commerce work on commodities?

Question

When you post a commodity such as a Radiant Ruby, you get to choose how many you'll be putting up for auction (direct buy really) and your asking price.

You are also presented with a sales average of how much people spent on that particular item yesterday.

When you attempt to buy a commodity, you just get a fixed price, not all the different offers.

So I'm left wondering about many things about the auction house, like:

• How does the auction house choose which player it "buys from" for each purchase.
• How is the asking price compensated (or inflated) related to the price the buyer actually pays.
• If the posted item's asking price is greater than what the buyer pays for it, does the AH put up the rest of the payment?
• Am I still going to get buyers if I place an item with a very high (or very low?) asking price?

The one time I sold any commodity on the AH it was tooth/essense from normal difficulty which I no longer had a need for, and they sold almost instantly, so I wondered what would've happened if I asked for more gold, for instance.

The AH is so simplified in this capacity that it confuses me about what the inner workings are.

Answer 1

Note that this isn't 100% certain, but this is how it appears to work from several commodity sales and purchases in the past few days:

• The auction house automatically purchases the cheapest items, but quotes you for the current average of the items within your quantity. If cheaper items appear between your search and your purchase, you'll receive a refund equal to the gold saved by not having to purchase more expensive items.
• If the purchase fails due to another player's purchase making your current gold insufficient for the quantity of items you want, the transaction will fail and you'll receive a full Purchase Refund.