This might be a bit tricky, but is definitely plausible.
First you find a merchant that can repair gear. When you click him/his name, you press the ESC button instantly.
So first press his name then milliseconds after press ESC.
If you have done it right, it will look something like this:
WILL POST PICTURE WHEN I GET HOME - You should be able to do this without a picture, lol
As you can see the Vendor menu is open and you also have the Game Menu open.
Now you press the Community button, after that is done, you press the find button. Now a new window will pop-up.
When this new window pops up, you press the X button up in the corner right. Now the game is basically frozen.
Go into the repair section of the vendor menu, and press repair. No money is taken from you.
And your gear is fully repaired. Now the issue is that when you leave the game, the repair costs come back, but if you do not leave game, you still have a fully repaired gear, even though you didn't pay for it.
I am not sure if the gear stays repaired after you exploit repaired it, since I didn't play much. Also the reason I am posting this, for people to test it out.
Don't waste your time trying to dupe with this exploit, it will not work.