Here's what you do (sorry if already posted, i'm new :S)...
1. Get or buy a twink item off AH.
2. Mail to an alt, who will then put it in AH for 10g.
3. Go back on main and say "WTB <insert item here>" 20g! (or whatever)"
4. Some noob buys the item thinking he's conning you to make profit.
5. The noob will /w you saying he has it or something.
6. Tell him someone sold you one already and apologise.
7. Go on alt and collect money :P
Some people may catch onto this if you do it too often...BE CAREFUL!
This is good if you have a twink item that is having selling problems.
PS. Might work on any rare, hasn't been tested yet.