first you need to know the tint laws in your state. in arizona for instance the darkest you can go on the front doors windows is 35%. from there back though you can paint the windows with krylon if you want.
as for the tint level you want, going with limo tint on the rear window is nice to hide things in the interior, but understand that it does make the rear window very hard to see out of at night particularly. personally i would go with what ever is legal in your area on the front doors, and go with 20% on the rears, if legal.
my taurus for instance has 35% on the front and 20% everywhere else.
one more thing, if you can, find a tint shop that uses formula one film, and step up to the pinacle film, it is the best.
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