Here is a test you can do to tell which part of the car needs tinting. Park under the sun for 5 minutes. Then touch the surface right below the glass where the sun hits. If it is hot that glass needs tinting, if not it does not.
I tested my model Y, only front windows and windshield lets heat in. Nothing else needs tinting.
I would not let a dude in a random shop to work on my windshield with so many sensors and electronics around it.
So I only tinted front windows.
Don't let tint shops fool you into tinting the rest of the car.