So, this idea would extend the feature-set of the auction house.

It would work similar to how the crafting request board works, but instead of requiring the mats for the crafting request, for an auction house buy order, you would specify the quantity of an item you are looking for (maybe an additional button could be placed in the folio), the amount you are paying per item, and it's really as simple as that.

There could be multiple buy orders up on the auction house at the same time - by multiple people.

People could partially or fully fill buy orders, depending on the item count in their inventory, and they could choose to fulfill one buy order over another (if there are currently multiple ones up).

If someone posts a buy order and there are already existing items for sale on the AH for that specific item, any existing item would be automatically purchased up to the quantity you specified in the buy order, assuming the already existing items for sale are less than the amount per item specified in the buy order.

If someone lists an item for sale (traditional method of selling items at the moment), and there is an existing buy order for that item (or multiple), and the price of the item being listed is equal or less than the amount of the existing buy order, that item would instantly contribute towards filling the highest priced buy order and instantly work as a sale to the person listing the item (assuming the requirements are met - price and quantity).

Placing a button to do this in the folio would be important because I and many other people are often looking for items that are currently not on the AH, but would love to grab up items when they come available - but we aren't always online. Buy orders would take care of this.

It would really round off the way the auction house works. People can already have items for sale while offline - buy orders would allow people to buy items while offline, or not actively searching the auction house for them.