Do a price check. Car-rental companies have been known to tack on surcharges without specifically informing customers. Late fees, early-return fees, and fees to change a reservation are just a few examples of the mysterious payments that can get added onto a bill. Double-check every item before handing over the keys.
Know where to book. Avoid booking directly with rental-car companies. Instead, opt for travel sites such as Travelocity.com or a service like Hotwire.com. Though Hotwire doesn’t reveal the rental company’s identity until you’ve committed, it provides a total price with fees and taxes included.
Talk to an insurance agent. The “biggest car-rental ‘gotcha’ is its highly profitable insurance.” You can avoid many fees by asking if your own auto policy has primary coverage for car rentals and opting for that instead.
Source: National Geographic Traveler