I think it is kind of realistic though depending on how you look at it. You do not sit in your stall and sell items all hours of the day. The system does or some imaginary character running the store. In real-life if you took some items to a store and asked for the shop owner to sell them on your behalf. If you came back the next day asked he give me the money from how many you sold plus all the others I can promise that shop owner would be a little upset and may even hold your inventory until you provided a bit of money. That rented stall basically works the same way you are signing up to dedicate yourself to selling those products.
I agree but it is a "player owned stall" implying that its rented and run by me. In terms of tax's they are applied when the sale is made not before. If we wanted to go even deeper there are plenty of vending machines that don't require personnel to run them that just sit back and sell things automatically. Although i think vending machines are a little advanced for this time period

. but that is how i view it. Also that is what i think the tax was intended for in the first place.