Currently the Goblin Rat trader takes all your meat and gives the XP, and then asks if you'd like to trade for anything. This means that if you end the conversation without choosing something to trade for, or end the conversation while you still have some "barter" left, you are unable to get anything back or "save up" for some of the nicer options.
Is it possible to make it so that the XP is given and the meat is taken when you decide what you want to trade for?
Well I'm certainly not going to mess with it, this is more complicated than it may seem.