Car rental agencies, such as Hertz, Avis and Budget, can offer travelers a wide range of vehicle models to choose from. But, what most customers don't need are a lot of the extra, pricey services—or the unexpected gotchas that appear on their bills at the end of their rentals.

Sure, there are the usual "full gas tank" options, which could be convenient for customers who would rather not worry about returning a rental with an empty tank. But budget-conscious travelers should probably think twice about the nicety, given the high fuel fees—and the surprising final car rental bill they could end up paying.

ShopSmart editors uncovered some of the other expensive charges consumers should be on the look out for when borrowing a car this summer. Watch the video and check out how to buck the trend of car-rental surprises and not get tripped up by travel charges.

And weigh in below: What's the most outrageous, unexpected fee you've had tacked on to your travel bills?