I found out a very simple way to sell an item for more than it is worth. This requires a BoE blue or epic item. I will use [Scamming Item] as an example. Here it goes:
Tell them you don't have enough money on this character and you need to mail some over from your main. Log out and get on the character which you put the item on the auction house from. The item should have sold at the high price(unless they already had the item).
First, make sure there aren't any other [Scamming Item]s on the auction house. If there aren't, post it at a high price, much higher than it is actually worth, let's just say 150g for this example.
Now hop onto a bank character (make another level 1 character if people know who your banker is).
In Trade-City, say "WTB [Scamming Item] for 200g". Now, after a while of you doing that, someone will look up [Scamming Item] on the auction house and see it there for 150g.
To them this is an easy 50g profit. Wait for someone to send you a message saying they have it, and check the AH to see if your item is still there. If it is, then they either already have another one of the item or are waiting for you to confirm that you want to buy it.
Tell them to come to you and trade it. If they do that and put the item in the trade window, they either bought yours or had their own.
Tell them you don't have enough money on this character and you need to mail some over from your main. Log out and get on the character which you put the item on the auction house from. The item should have sold at the high price(unless they already had the item).
Wall of text fixed.