Clean the inside of the windshield. I snag a paper towel, or a bit of moistened newspaper will do.
Rental cars run to pretty new. The plastic upholstry "blooms" plasticisers, lubricants and other chemical junk that makes up new car smell. The chemicals plate out on the inside of the windshield. Pretty soon the windshield has a film like a 2-pack a day smokers windshield. The first time one meets some nipplehead with blazing high beams the film turns opaque.
Somehow, not even the majors clean the inside every time.