Gadgetzan AH (WoW), exact same as Nar Shadda GTN.
Also, its not an exploit, you put it up on the GTN, it sells or not thats working as intended, so what if its your own character. You could have just grinded the creds on the other side anyway... I found 99 mand iron on the Nar Shadda AH for 100 cr. someone was obviously trying to transfer it across factions, I can imagine how mad they were when they found it not there... ps I was quite happy.
Personally I think you should have been restricted to one faction per server, but I guess they didn't do that so that the legacy system was more attractive idk.