The most common scam we have observed at rental counters is an attempt to scare senior travelers into buying "insurance" they don't really need. The main culprits are collision- or loss-damage waivers (CDW or LDW) that relieve you of financial responsibility for damage done to the rental car while it's in your possession. That coverage can easily add up to $15 a day to the rental - sometimes more. And, these days, even with those stiff rates, you may encounter a "deductible" that still leaves you on the hook for up to the first $500 in damage.

Fortunately, many drivers are covered for collision damage without having to buy anything extra. Your regular auto insurance may cover rental cars. Also, most Gold MasterCard and Visa cards offer automatic no-cost collision coverage, as do most American Express cards and all Diners Club cards, when you use that card to rent the car. Either way, in most cases you can confidently decline the rental company's waiver.

(To be sure, before you book, check with your own insurance firm and/or credit-card provider to see exactly what your coverage is.)

Nevertheless, we've seen rental agents try to scare senior renters with statements such as "you don't want to drive without insurance, do you?" or even, "I can't let you off the lot without insurance."

If that happens to you, be firm: If you know you're covered already, refuse the coverage by initialing the "declines" box on the rental agreement.

These days, city governments around the world have zeroed in on people who rent cars as a happy hunting ground for taxes and fees.

We recently reserved a rental on which a series of extras added more than $20 to what was nominally a $60 rental bill. You can't blame the rental companies for those fees - they're just passing them along - but they can be a nasty shock when you think you've arranged a low-cost rental.

One fee you can avoid is that for extra drivers. Most big companies, at most locations, don't charge any more if you want to share driving with your spouse, or even with a son or daughter. But some companies, at some locations, sock you as much as $10 a day for an extra driver. That's an inexcusable gouge: Adding a driver doesn't increase the rental company's cost or risk by a penny, let alone $10 a day.

If you plan to share the driving, ask about extra driver charges before you commit to the rental. If the company says it will charge you, shop around for another company that won't.

Most of the rental-car recommendations we see are based on the assumption that you'll be renting as a separate transaction. But that isn't always the case. Many senior travelers rent a car as part of an air-hotel-land package tour. And that arrangement raises a bunch of complications. The package price almost never includes taxes and fees, so you'll be on the hook to pay them as extras. Since you can't shop around for a better deal, the rental company may take advantage of your "captive" status to throw a much higher than usual extra driver charge at you.

If you rely on a charge card for CDW/LDW coverage, make sure it will cover you for a car that's bundled into a package tour.

Call the customer-service number for you card and ask specifically whether collision coverage works in that sort of arrangement - especially if, for some reason, you didn't use the card to pay for the tour package. And even though your rental is prepaid, you can expect the rental company to slap a "hold" of several hundred dollars on your card. Make sure you have credit to cover that and trip expenses.

Remember, some rental agents view you as a sucker waiting to be fleeced. Know what you do need to buy and what you don't, and stand your ground.