Smoking weed in a car rental could be a very expensive move. Rental car companies will charge you a fine for smoking or vaping in rentals, some up to $400. But if it’s unavoidable - roll down the windows to air it out, get yourself some Febreze and apply liberally, and add in the baking soda and/or vinegar odor-absorbing options. Consider a cleaning service if the smell is really bad.