Although there is a possibility that somebody bought and returned the car, and the buyer tinted it, normally he/she would have tinted all windows not just back one.
I have seen Toyota's cars having darker back glass. You can easily verify this by looking at the edge of the back glass, particularly upper edge for any indication of after-market tinting.
I have seen Toyota's cars having darker back glass. You can easily verify this by looking at the edge of the back glass, particularly upper edge for any indication of after-market tinting.