I found a huge bug in the Playstation 4 version o the game :
To make it short, you can barter nothing for anything (a tomato for 10 skill book).
Here is how it is made :
You open the barter window from a vendor. In the vendor offer window, you select what you want (ex: 10 skill books). Now, you wont put anything on your offer window but instead, you just switch on the "give for free" window and there, you select whatever object you want (ex : a tomato). The merchant will always accept your offer, no matter what.
It is really game breaking as it broke all the economy system. Gold are now useless. Also, it broke the personal reward mechanic and to an extend the sense of progression of your party since you don't need anymore to save money to buy something interesting. You are no longer forced to make choice since you can have anything you want, equipment-wise.