* Avoid casual operators. There are small companies that simply rent out a private owner's Lamborghini or Bentley and take a commission, which for them avoids a lot of insurance and financing hassles. But it means that if you crash it, you bought it, since neither your insurance nor the owner's will cover the damage. Another problem with such fly-by-nights is that the owner can suddenly decide he needs the car more than you do and capriciously cancel the "rental."

* Beware the stock photo. Anybody can put up a fabulous photo on a Web site, but the beautiful Ferrari F430 roadster you see depicted (a shot probably cribbed from Ferrari) can turn into a tired, mistreated old F360 coupe when you pick it up. Some small rental agencies even trade cars back and forth, and the new Lambo you thought you were renting can end up being a Corvette. Explain that to the prom queen.

* Ask for a thorough briefing before you drive off. I once borrowed a press Ferrari that was given to me with a quarter tank of gas. When I finally stopped to refuel, the low-fuel light glowing, I couldn't for the life of me find the fuel-door release, and the car had no owner's manual. It took me 20 minutes to find the toggle switch, and nobody else could help, because cars like this can be configured totally differently than anything one has ever driven.

* Know the rental's limits. How many miles are you allowed, since exotic-rental companies never offer unlimited mileage, and how much does the extra distance cost? What happens if the car breaks down? Are you out big bucks if an overstressed Aston Martin engine decides to swallow a valve on your watch? Who do you call for roadside service? What if the freelance tow truck carelessly breaks the $15,000 carbon fiber front air dam? What damages are you responsible for? Remember, these aren't bulletproof Chevys or Toyotas. They're in some ways delicate; that's why they're called exotics. Don't believe it? Noah Lehmann-Haupt, the founder of Gotham Dream Cars, recently had his own $170,000 Ferrari F360 burn to cinders on the verge of a New York parkway when some fuel leaked and ignited.

* Be careful what you sign for. Like cowboys' ponies, high-performance cars get ridden hard and put away wet. Clutches are abused, tires are spun and slid, engines are regularly run to the redline just to hear the exhaust wail. Small rental agencies don't have facilities to keep these cars well-maintained, and often they're simply brokers borrowing the car from another firm or a private owner. You may have just signed for a 505-horsepower Corvette ZO6 with a clutch two shifts away from turning into a grenade.

Here's one warning I'll add to Gotham's. Because ground clearance is minimal and soft alloy wheel rims often extend outward farther than do high-performance tires, a driver unaccustomed to supercars typically does two types of damage: whacks an expensive front spoiler against a driveway lip, or rubs a wheel on a curb. And these wheels can easily set you back $1,000 or more each.