You might ask the charlatans at that dealership how “permanent” this bit of latter-day snake oil actually is. The name, Perma Plate, is intended to give one the impression that this incredibly expensive car wax is long-lasting, if not permanent. Ask for a written guarantee of its permanency. More than likely, there is no written guarantee as to how long it will last, and that is because it is just VERY overpriced car wax.
Unless you enjoy wasting your money, I would suggest that you forego this offering as well as the “upholstery protection” and the undercoating that they will also try to sell you. When I buy a car, I make it very clear that I will not buy a car with a “dealer pack” (dealer-installed tape stripes, wheel well mouldings, etc.) and that I will walk out if there is any attempt to upsell me after I have settled on a price. And, I remind the salesman of that fact several times.
I also refuse to have a dealer sticker or emblem placed on my car. I make these terms very clear, and I also hand the saleman a piece of paper with MY final price written on it–and I remind the saleman that it is final–no ups, no extras. I tell him (or her) to get approval from the mythical sales manager quickly, because I am prone to walking out if I am kept waiting for an extended period of time.
If this dealership is successful in getting you to buy this vastly overpriced car wax, then you have essentially given up whatever price advantage you thought that you had gained when you negotiated the price downward from the list price.