Just look e.g. at how shops work (and to which for some reason we are accustomed):
- It is _not_ typical that wares are lying on the ground.
- It is _not_ obvious that picking them up doesn't steal them but rather puts them into a kind of cart.
- It is strange that a shopkeeper blocks a door and moving into him just brings up an attack option.
- It is weird that you can talk to the shopkeeper but this doesn't lead to any meaningful interaction.
- It is bothersome that you need up to three separate commands to pay (p to pay single items, P to display your debts, :p to pay for all; not to mention that you need the fourth ($) to see your gold because our gold icon in the new HUD is so tiny that nobody understood it).
- It is strange that a shopkeeper sometimes doesn't immediately clear the door to the shop after paying but keeps it blocked for a moment.
- Villagers running around in the shop and standing in the way also aren't helpful.

We could get rid of all four commands, replace it by "p"ay, not require to be anywhere near the shopkeeper for it to work, display a dialog that lists your debts, your current gold and offers to pay for (1) all, (2) some items or (3) none right now. And then just execute the transaction or allow you to select the items you want to pay for (optimally in a simple multi-select-variant of the pick-drop-dialog which we yet don't have). Or you would be press "p" and display a window featuring your current gold, plus any items you have to pay, and just pick from the list with keys/mouse. Items that are not affordable should be gray and emit that annoying buzzing noise of no-can-do. Adding an (x) close menu button would be a nice touch, just for those "I don't know what to do neeeeeext" kind of guys.