First of all, it would be great to be able to buy and sell large objects like barrels or workstations from barter stands. It's a bit annoying to buy drinks by the bucket, y'know? Perhaps special barter stands could be implemented for this since you can't put large objects in cabinets.
Second, we should be able to buy and sell hats from stands. Right now it's possible for a vendor to put a hat on a stand, set a price and scam people out of their money since you can't transfer hat this way.
Third, I noticed that when a vendor wants to buy something expensive like a game time token from their barter stand, their only option is to put multiple stacks of coins in a present box and label it with what's inside. Of course, they could lie about the contents of the box and scam others this way. A transparent box would be really useful to counter this. Then buyers could be sure that they're getting what they paid for.