All seven of my neighbor's cars have had dealer plates, for months. Illegal?

So about three months ago a new family moved into a house down the street from me. I thought nothing of it but being a car person, I started noticing that they always had different cars.One day a black C350, the next a silver Escalade, the next a white XJ, and so on. The catch is that every single car had the same dealership license plate frame and paper plate that stated the dealership name.Now for the past month, they have continuously had in front of their house or in driveway:Ford EdgeJaguar XJBMW 750Mercedes E350Nissan AltimaFord ExplorerLexus ES350All of these have the same exact dealership paper plate, and I see them using these cars for personal use (I've seen them return home with kids jumping out just getting home from school)Considering there have been different vehicles at this house within such little time, I highly doubt they personally own them. So I'm beginning to wonder is this an owner of a dealership using cars for sale as personal vehicles? Is this legal?Edit: I'm in CA and I want to make it clear this is purely out of curiosity. via /r/cars http://ift.tt/2tVoocF