Q:

How long do I have to change my mind (buyback)?

I've made use of the buyback feature a few times already, but I was wondering how long items remain in the buyback tab before disappearing. Is there a time limit, or do they last until you log out?

A:

From my personal experience, merchant buyback has only cleared when I leave the game. 
There is also a hard limit of the last 12 items sold on a merchant. The buybacks are shared between merchants, too.

