Renting a car can be expensive if you’re a tall person because you’d want to rent a standard or intermediate car to allow leg-space, which usually is not the case with a Economy option. Budget Travel suggests that there’s an easy way to upgrade your rental car.
Book the cheapest car and hope that they sell out fast, then the rental company has no choice but to upgrade you. That said, Budget Travel recommends you stay firm in not paying for an upgrade:
The check-in clerk may try to sell you an upgrade for a discounted fee. Say no. If they don’t have the car you reserved, they usually give you a better model at no extra charge. Arrive early in the day, before most people return their cars, for the best shot.
This may not work every time, but careful planning might turn that small Economy car into a spacier mini-van.
Read more at: How to Get a Free Upgrade – Budget Travel