If you're like most Americans, you've probably rented a car at least once in your lifetime. Although rental car companies typically cater to business travelers and tourists, some advertise rates so low that you may be tempted to rent a luxury or sports car just for a weekend of fun. Regardless of your reasoning for hopping behind the wheel of a rental, take the time to educate yourself on the car rental industry before you sign the paperwork. Doing so helps you avoid the financial strain of falling wallet first into an advertising loophole.

“There's a good chance we won't have the car you reserved.”

While most major car rental companies allow you to make online reservations ahead of time, reserving a rental car online doesn't guarantee that the car you selected will actually be available when you come to pick it up. Rental car companies are in the business of making a profit. The more time a rental car spends off the lot, the more money the company makes.

While you can't force your rental company to hold a specific vehicle for you, you have the right to demand that the company upgrade your rental for the same price. If you end up renting a cheaper vehicle because of availability issues, make sure that the company adjusts your bill to reflect the lower rate.

“Our advertised rate doesn't exist.”

You've probably seen rental car commercials and advertisements that boasted shockingly low rates for rentals. If you try to take advantage of those low rates, however, you'll quickly learn that the advertised rate comes with stiff restrictions. For example, the company may require that you rent the car for a minimum number of days to qualify for the deal.

Keep in mind that the advertised rate does not include taxes and fees. Rental car companies are infamous for tacking on numerous fees. Depending on where you rent the car, excess fees can increase the cost of your rental by 30 % or more.

“We'll overcharge you for gas.”

Your rental car company makes no secret of the fact that, if you don't return your rental car with a full tank of gas, it will charge you to fill up the tank. What you may not realize, however, is just how much rental facilities charge for gasoline.

In 2011, most major car rental facilities charged consumers between $7.99 and $10.00 per gallon – far more than the actual price of gasoline. In addition, some car rental companies charge a refueling fee based on the number of miles a renter drives. If you rent a car from a facility that charges a refueling fee based on mileage, you'll be charged for a tank of gas whether you fill up the tank or not.

“You might not need our overpriced rental insurance.”

Car rental facilities often push consumers to pay extra for rental insurance coverage. Rather than risk being held responsible for thousands of dollars in damage to a rental car, many renters give in and pay fees of up to $40 a day to protect themselves.

Unfortunately, buying the rental company's insurance is often a waste. If you have full coverage insurance on your personal vehicle, there's a good chance that your insurance policy covers rental vehicles as well. Review your policy to verify what your insurance provider does and does not cover. If your car insurance policy carries over to rental vehicles, you can safety turn down the rental company's steep insurance fees.

“You can reserve a car, but you have to pay extra to drive it.”

Just because a rental car facility allows you to book a car rental online, that doesn't mean that you're approved to actually drive the vehicle. More and more rental car companies are charging underage driver fees to renters under the age of 25. The rationale behind this fee is that younger drivers are less experienced and more likely to get into an auto accident. Don't expect the rental car facility to inform you about this fee up front. You aren't likely to discover that you paid extra simply for being young until you return the car and review your final bill.

“You can cancel your reservation, but it will cost you.”

If the rental car company does not have the car you reserved, won't honor its advertised rate or you simply find a better deal elsewhere, you might have to pay extra just to cancel your reservation. In the past, most car rental companies did not charge consumers a fee to cancel a reservation. This wasn't generosity. Because most people paid for their rentals when they picked them up, car rental companies had no way to force cancellation fees on consumers. Now that reserving a car online with a credit card is an option, the car rental company has your credit card number on file. If you cancel your reservation, the company can – and probably will – charge you a fee for doing so.

The best way to avoid the hassle of car renting is not to rent a car in the first place. If you can't avoid making a reservation, shop around for the best rates before settling on a rental facility. When you pick up the vehicle, ask for a copy of your bill. Review the bill carefully before signing on the dotted line. Ask questions about any fees you don't recognize and, if there's a problem, don't be afraid to ask for a  free rental upgrade as compensation.