Note: I have not actually done this and "scammed" someone but I have a feeling that it will work based off of the experience I have had in buying items cross faction.
What you will need: Characters on both factions on the same server
Basically the goal here is to have a player post something on the neutral AH for a low bid regular buyout. What you'll do is find something that you can easily get someone to sell you, such as plans, designs, epics, or blues, but say that you play the other faction and need it posted on the neutral AH. Some people will shy away from this since it takes a 15% cut of what the item is sold for, so you can tell them that you'll compensate them for it by paying 15% more. Now that you have got a person willing to sell you those items, they'll go and post them on the AH. This is where people get a bit sloppy. I'd say over half of the time they put it up for the default bid, only altering the buyout since they know they've got the sale. Also, people put things up for the shortest duration generally thinking that it saves them money since the deposit is cheaper. So you have something posted up for a cheap bid and the shortest of the 3 AH durations. Now, all you have to do is snipe it.
It would have worked better back when you could do 8 hour auctions, but yeah ...
Also, if this is a repost, sorry for wasting people's time. I didn't thoroughly check to see if it was previously posted because to be honest I don't really care enough to. So that's about it ...