Unscrupulous practices conducted throughout the auto industry topped the list of consumer complaints last year, beating out home contractors and other frequent sources of gripes nationwide, according to a review conducted by the Consumer Federation of America.

Automotive complaints didn't even make the Top 5 the previous year. Now, they surpass the likes of shady home-repair businesses, predatory lenders and slumlords to claim the unwanted title.

"Whether it's an offer on the internet or meat being sold door to door out of the back of a truck, consumers need to be careful in today's marketplace," said Amber Capoun, president of the North American Consumer Protection Investigators.

Automotive-related complaints included everything from used-car salesmen rolling back odometers and then selling high-mileage cars to unsuspecting customers to deceptive advertising.

Examples of recent fraud

- In Florida, an elderly woman paid $1,141 to have her transmission repaired. It still didn't work right, so she took it to a second repair shop and learned she needed to have the entire transmission replaced. The second shop charged her $500 for the diagnosis and left the transmission in pieces.

- In Georgia, investigators found that one used-car dealership had rolled back odometers on at least 17 vehicles, then sold them to unsuspecting customers. Based on the investigation, duped buyers received refunds or compensation for the lowered value of the cars.

- Auto financing scams and repossessions rank high among the auto-related complaints. In Ohio, a family's car was repossessed after falling behind on payments. Because of problems with the original contract, the state's Attorney General's office had the repossession reversed, penalties nullified and got the consumer a check for $200 to compensate them for their troubles.

- In New Jersey, a woman returned a leased vehicle in immaculate condition – she took pictures to prove it. Nonetheless, a few months later, she received a $1,600 bill for damage to the vehicle. After much legal wrangling with out-of-state departments, the dealership finally dropped the complaint upon realizing New Jersey law gives customers the right to get an independent appraisal for any damage.

Fastest-growing problem: Tow trucks

Some of the biggest complaints involved lemon laws, in which customers say dealerships refused to rescind sales on cars that were falling apart as soon as buyers drove them off the lot.

CFA proposed that lawmakers prohibit – or at least limit – "as is" sales on used cars to protect consumers from these types of situations, saying it also protects the interest of honest car dealers who are at a disadvantage when they sell high-priced cars with warranties.

The CFA culled its information from a survey of 40 state and local consumer organizations and government entities, which provided 360,358 complaints. It says consumers received $97,832,511 thanks to mediation from these agencies.

Across any industry, the fastest-growing complaint category was unscrupulous towing practices. Last December, the New York Post reported that tow-truck operators in New York City had been towing away legally parked cars and scamming owners out of cash. In some cases, they had targeted victims of Hurricane Sandy. These two-truck operators are especially hard on tourists with out-of-state plates who the perpetrators bet are unfamiliar with local parking laws and will pay up just to get their vehicles back.

Crooks started using other new scams in 2012.

In Maryland, a company collected and posted information about drivers' minor traffic convictions on a website, and implied the offenses were more serious criminal matters. They offered to remove the information for a fee.

How you can protect yourself

When dealing with repair shops and dealerships, here are a few tips for avoiding problems:

- Get a second opinion. Although you may pay for a mechanic's time, you should get a written estimate for both repair bills and diagnostic fees so there are no surprises. If the repair seems to be very expensive, and something you think should be covered on warranty, then research the problem online by Googling your car and the specific problem. You may have success challenging the cost with the car company's regional customer-service rep.

- Buying a used car? Buy a vehicle history report, such as CarFax. You'll find a list of approved companies that sell them at www.vehiclehistory.gov. Keep in mind, however, many of these reports, while helpful, are only as good as the information reported to the agencies that collect them.

- When you return a car at the end of a lease, keep a copy of the lease agreement, note the mileage on the car and take photos and/or video so you'll have proof of the condition of the vehicle.

- If you're buying a car, have it examined by a mechanic you trust before signing on the dotted line.

- When financing a car through the dealer, don't be pressured into signing the agreement right away. Take the time to read it. Ask questions.

Pete Bigelow is an associate editor at AOL Autos. He can be reached at peter.bigelow@teamaol.com and followed on Twitter @PeterCBigelow.