Ditto
The dealership is attempting to sell you a grossly overpriced coat of car wax.
In other words, what you can do for an investment of about $10 and a few hours of your time will cost–most likely about $200 or more at the dealership.
Likewise, the fabric protectant that they will likely also try to sell you is simply Scotchgard, which you can spray on the upholstery for a fraction of the price that the dealer would charge you.
And, if they attempt to sell “undercoating” or rust-prevention treatment, bear in mind that these products have the potential to hinder the action of the very effective rust-proofing that the car got at the factory.
If the salesman attempts to tell you that the paint will deteriorate without the “Glass Coat”, I suggest that you tell him that you have changed your mind and do not want to buy a car that comes from the factory with such a poor-quality paint job. Use a similar response if they attempt to sell you the fabric protectant or undercoating.