you're right. it should look good, and the testers will make sure that it looks "professional".hope it wont look ride to say, Its kinda good idea yet it would be better if we make the mechanism bit professional too, for example: each day our merchant introduce a list of items and players will choose max 3 items for that day ( choices and list will be resets as the main idea suggested so the list contains same items.
I will complete my idea. the player approaches the trader and a dialog box appears, for example (I'm not good at this)
the player: hello, trader
NPC trader: Hello, (nickname). today I have such an assortment.
at this stage, the inventory is displayed in it, as in the store.
it would be good if the seller offered things that are not available in regular stores. (for example, ingots, 2K items, drops mobs)