American Express will not cover a car rental of more than 30 days. Visa is usually 15 days. Depending on the card, MasterCard ranges from 15 to 31 days. Some credit cards don’t provide international coverage. For example, Visa excludes Ireland, Israel and Jamaica.

Almost without exception, a credit card provides “secondary” coverage. If you get into an accident or something happens to the rental car, your credit card issuer is going to insist you first run any claims through your personal insurance. Only then will it kick in and pick up the “extras.”

Harzog is a fan of American Express’ Premium Car Rental Protection. It’s available with most AmEx cards. For an additional $24.95 (that’s per rental) you get up to $100,000 of primary coverage for damage or theft of car, up to $100,000 of accidental death or dismemberment coverage and up to $15,000 for excess medical expenses. Your car rental period is extended to 42 days.

The biggest selling point? “Coverage is primary,” says Harzog. “That means if anything happens to your rental car, you don’t have to file a claim with your personal insurance company, pay any deductible or risk having your premiums increase.”

No matter which credit card you have, one thing is paramount. You must use that card when renting to activate the coverage. And, points out Harzog, if you buy the rental insurance, that negates your credit card coverage. So no double dipping.

TO BUY OR NOT TO BUY?

Back at the car rental counter, that agent is still asking if you want to buy insurance. And the answer is ... probably not.

Brower says the only time to buy at the rental agency is if your policy doesn’t cover rentals, has a high deductible or does not include collision coverage or sufficient comprehensive coverage (which helps pay for loss or damage to a vehicle not caused by a collision, but vandalism, theft, hail or similar).

“Even if you don’t own a car and therefore don’t carry auto insurance, take your time at the rental counter,” advises Brower. “Consider the packages being offered. You may not need the most expensive plan.”

Bottom line: Weigh the pros and cons. Should you rent a car and get into an accident or the car is stolen, the rental agency considers it your fault. If something happens and you opted out of rental insurance, it may reflect on your personal insurance record. And there may be the hassle factor of dealing with paperwork or your credit card company.

But never feel pressured to buy rental car insurance. “It’s optional,” emphasizes Paula Rivera, a spokeswoman for Hertz. “You are not obligated to take any car rental optional package. And no agent should tell you otherwise.”

Have a solid understanding of what you have and you’re on solid ground.

Laura Daily is a consumer travel strategist and executive editor at LivingOnTheCheap.com