I dont know if this has been said, but there is a bug where when you have an item on the counter while handing the customer their weapon, they take the one on the counter instead... but the game still thinks you sold the item they actually wanted. the item they were supposed to take is left behind too.
are you sure about that? I think for me the game actually paid me the weapon that the customer took. I got paid a great sword (which they took) even though I held a pole arm into their face
Edit: And yes, it has been reported somewhere xD sooooo should be fixed in the next patch maybeee?
I am aware of the issue. I'll be working on a fix for that.