Did a search and could not find anything related to this exploit.
Most people who enjoy fishing probably know about the Weather-Beaten Journal (Weather-Beaten Journal - Items - World of Warcraft) that you can get when fishing various pools. The journal is found inside various boxes you may get when fishing and is in itself BoP, though while you can't loot a second one after learning the find fish skill (nor can you see if your box contains a journal) it is still possible to sell them to other users.
So how do you identify if your box contains a journal? Easy, make an alt and learn the fishing skill on it, then simply mail all your boxes to that character(but be careful not to open them with your main, as that will delete the journal from the box). That alt will now be able to open the boxes and see if there are any journals inside and can then sell the boxes to other players, since they arent BoP.
Enjoy