I think that the realty npc just shouldn't say if something is being rented. you would have to click the rent button with the cash on you to see if its being rented or not. if you rent it, its obviously not being rented. if it is being rented and you go to click the rent button, nothing should happen, it probably shouldnt even say that you cant rent it cuz someone else is renting.
We hope to see you online soon!