While most used-car transactions come off without a hitch, there are spectacular exceptions.

Consider Alisyn Studeman, 22, of Big Lake, who had owned her red 2002 Nissan Sentra for about a week when, while driving down Interstate 94 last summer, the car began to smoke. Studeman pulled over and within minutes the car was engulfed in flames.

She came away with her life, but lost her purse, camera, cellphone and the $5,400 she had just paid for the now-smoldering chunk of metal. Unfortunately she had bought the car "as is" and had no recourse with the dealer.

Jeannie Stone bought her 1996 Chevrolet Cavalier "as is" for $1,995 from an Anoka County dealer on June 19.

"It blew up on June 22," Stone said.

Stone said that she was driving down the freeway when the car started losing velocity and began to knock. She had it towed to a mechanic who found "bearing links broken, no compression in the engine, and something fried," she said.

The dealer was not interested in negotiating relief for her "as is" purchase, she said. "That was all my savings. I'm on Social Security disability and I only have liability insurance."

No warranty for 'as is' cars

While a quarter-century-old state law requires an automatic warranty at dealers' expense for certain used-car purchases, many cars are sold "as is" because they are too old or worn to meet the warranty's conditions.

It's a sign of the times. Owners are holding onto their new cars longer; the average age of cars on the road was 10.8 years in 2011, an all-time high, according to R. L. Polk & Co., a Michigan automotive research firm. Cars were about eight years old on average when the warranty law was enacted.

Attorney General Lori Swanson's office describes the Used Car Warranty Law as "one of the strongest" in the country. Under the law, a dealer must repair or replace certain parts that fail within one or two months of purchase or refund the purchase price. This warranty need not be mentioned to be valid.

However, if a vehicle has at least 75,000 miles on it, is at least eight years old, is sold for less than $3,000 or meets any of seven other criteria, a dealer may sell it "as is." In that case, once you buy the car, it's yours, warts and all. Contrary to popular belief, there is no three-day cooling-off period. Nor does any lemon law apply to cars with expired factory warranties.

"I would say the biggest misnomer is the lemon law. People think that there's a 30-day lemon law," said Dan Belawski, general manager of Alex Used Cars in Minneapolis.

While Alex Used Cars has no written warranty, the business will help buyers of "as is" cars get as much as 50 percent off repair work, Belawski said.

Mark Lutes, who works for a Bloomington dealership that sells new and used cars, stressed the buyers' responsibility to take ownership, so to speak, of their "as is" purchases. "The fact is when someone has a problem, they don't tell their friends they bought an AS IS car, instead they say the dealer ripped them off," he said in an e-mail.

Do your research

The attorney general's office has a number of suggestions for used-car buyers. Before a car becomes irrevocably yours, it's best to make sure you want it. Read the "buyers guide" that, by federal law, is posted in car windows and contains warranty information.

Test drive the car and put it through its paces. Brake hard. Take it up to highway speed. Drive in reverse. Turn the radio off to listen for strange noises.

Ask for everything in writing. The spoken word is hard to introduce as evidence of a promise made.

Get a third-party inspection. The dealer should either let you drive the car to a mechanic or take it there for you. Either way it's at your expense. A survey of three metro-area repair shops found their inspections range from $30 to $90.

Minnetonka Auto Service charges $59.99 for a 100-point inspection, said owner Howard Bazinet. "I've had more than one person fall in love with a car, and then not buy it" based on the inspection, he said. "The $59.99 can save you the headache of buying a car that's headed for the junk yard."

Mason Crowley, 16, of Rogers, probably wishes he had at least tried to take a truck to a mechanic before buying it. The truck would not have made the trip.

In July, he paid a dealer in Savage $800 for a 1996 F150 pickup. Five minutes down the road, "white smoke went everywhere" from a burst coolant line, Crowley said. He fixed it, but one mile later the truck expired from a cracked engine block, he said.

Industry better than before?

"Complaints against used-car dealers are often high on our list -- sometimes topping our list," said Dan Hendrickson, spokesman for the Better Business Bureau of Minnesota and North Dakota.

"But to their credit, many used-car dealers do go above and beyond what would be expected of them to get the customer moving again," he said. Car "dealer ratings largely fall into line with ratings for other industries."

"I have been selling cars for almost 20 years, and I can assure you the used-car business has changed for the better," Lutes said.

The attorney general's office offers practical advice in the form of a handful of car-specific publications including "The Car Handbook" that explains the Used Car Warranty Law. Call 651-296-3353 or go to startribune.com/a1716.