Prepare your car for the summer
This may sound a bit gross, but unfortunately it's quite a valid point. Fabric seats are prone to stains in the summer, especially from excessively sweaty occupants. Summer months also bring extra dust with them, which tends to enter the car cabin along with passengers.
While we won't go as far as going the taxi way and covering your seats with towels, you can however maintain fabric upholstery with regular dusting, vacuuming and an occasional shampoo from a pro car wash.