How about when the rental company tells you they are out of cars in the category booked but are going to upgrade you, no charge? Usually, but not always, that’s a pleasant surprise. Sometimes instead of a VW Golf you get a Mercedes Benz. More often, however, it’s a sedan to station wagon; harder to park and burns more fuel. What if your upgrade is to a fuel-hungry SUV and you’re planning to do a lot of driving?

Unfortunately, such upgrades are within the rental company’s reservation policy. The company fulfilled its promise by giving you a car in a category equal to or better than you booked. When that happens your options are twofold; argue or find another company.

Some voluntary upgrades have the potential to cost you money. Take Jim and Susan. They booked a seven-passenger van for pickup in Germany. They paid in advance with a Visa card that provides free collision and theft insurance coverage. At the rental counter, however, the agent handed them keys to a nine-passenger van.

It wasn't until they were on the road that they noticed the vehicle had nine seats instead of seven. At this point, alarm bells should have gone off. But, sadly, it didn't occur to them that the larger van might not be covered by their credit card’s free insurance policy. By now you've guessed what happened. The van got a $1,000 fender scrape, Jim and Susan applied to Visa for reimbursement but were denied because nine-passenger vehicles are not covered by most credit card insurance (an exception is Amex’s preferred car policy which costs about $25 per rental).

Beware, too, of proffered upgrades to such cars as the E-Class Mercedes, 5-Series BMW, or Audi A6. Autos that retail for more than $50,000 are typically not covered by most credit card insurance.

You can protect yourself against this sort of upgrade by paying for your rental car with an American Express card and purchasing its Premium Car Rental insurance for $25 ($18 for California residents). The program provides primary coverage, offers $15000 in medical coverage, insures rentals as long as 42 days, and covers most high-end rental cars that normal credit card insurance does not, including the popular 9-passenger standard van. If you’re renting a car in Europe, it’s definitely the coverage to have. Obtain the coverage here.

Get a written quote on a car rental in Europe.