We forgot to ask when we bought our house. The water heater is plastered with warnings, 'This is a rented machine', etc. I called every one of the six phone numbers on the side of the thing (gas installer, water heater maker, water heater installer, water heater maintenance and service, rental company, etc. etc.) and not one of them had any record. The sellers couldn't even remember if they had bought it. After five years in the house, no one has come knocking. I'd almost relish the fight I'd have if anyone ever attempted to collect on me (statute of limitations, my name not anywhere on a contract, etc.)
But yeah, I'd buy the damn thing outright just to not have anything hanging over me.