Secondhand car dealers have been given a rough ride in a report on their activities by the Office of Fair Trading.
The watchdog found that one in five people buying a used car from trader discover they have a problem with the vehicle.
Many of these issues arise within a month of the car being driven off the forecourt.
For many consumers, a car is the second most expensive purchase of their life, after their home. So what can they do to protect themselves from a rogue salesmen and what are their rights?
What general tips can you give me?
UK consumers buy 3.6 million secondhand cars from car dealers each year, spending a total of £24bn.
They have more rights by buying from a dealer than if they bought privately, but they pay a premium for this extra protection. This OFT report questions whether they are getting the service they expect.
But buyers must be honest too about what they are buying. The report found that some have "unrealistic expectations" about the condition of a car, given the age, mileage and price charged for it.
Alistair Jeff, director of sales for Carsite.co.uk, says: "People spend a lot of time and effort looking to buy the cheapest car.
"But the best value car is a good quality car, at a good price, from a dealer that is willing to give you back-up and service."
Many people spend a lot of money but do not actually have much of an idea about what they are buying. So take somebody along who knows what they are talking about.
Any specific things to look for?
You can get any vehicle independently checked, test drive it and look at all the relevant documents.
But the Retail Motor Industry Federation - the trade body for the industry - also suggests going through an inspection check list.
This includes: checking the underside and bodywork, making sure tyres have the correct tread of 1.6mm or more, ensure paintwork is in good condition, make sure the locks work, and check all the rubber seals including windscreen wipers and doors because leaks can be expensive to fix.
On the outside, make sure that no panels are a slightly different shade, or rippled, or uneven, or heavily chipped by stones.
The inside of the car can give clues about how well it has been treated and whether the mileage is accurate.
So look at the state of the seatbelts, see whether the carpets are in the condition you would expect, and look at the milometer, dashboard instruments and pedal condition.
What laws and rights am I covered by?
The Sale of Goods Act 1979 is a key right for consumers buying anything from a trader, not just a car, and says that the item should be of satisfactory quality, or as described.
Under the Sale of Goods Act, the dealer should resolve the problem, with a refund, repair or replacement if the vehicle was defective when sold, unless the defect was made clear at sale.
For the first six months, the retailer must prove the product was satisfactory when bought if they turn down a replacement or repair.
For the next six months, the consumer must prove there was something wrong on purchase to get a replacement or repair.
The other key rights come under the Consumer Protection Regulations (CPRs) that came into force in May 2008 and replaced the Trade Descriptions Act. These state a general rule that traders should not operate unfairly.
The OFT says that these laws are adequate to tackle any rogue operators.
How does this work in practice?
The "professional diligence" test under the CPRs mean that buyers can reasonably expect traders to carry out pre-sale checks in relation to the history, mileage and mechanical condition of the car.
They should also provide after-sales service, listen to complaints, and never try to hide behind illegal disclaimers that suggest there are "no refunds" or the car is "sold as seen".
Car clocking is illegal, but often difficult to spot. You can check mileage, for a small fee, with services such as the HPI check or CarDataChecks.com .
A car which is more than three years old must have a MOT certificate, a full service history is worth checking and a reputable trader should check the car's financial history.
More information is available through the MOT information website .
The OFT says that as a matter of good practice, important information about the vehicle should be put on a checklist displayed in the vehicle, such as if it is ex-rental.
"It is important that consumers are asking questions about what checks have been made in advance and it is very helpful to get that information in writing before they purchase the car," says Peter Lukacs, of the OFT.
"If there is a problem afterwards, they can more effectively go back to the dealer and state their claim."
What do I do if I still have a problem?
Don't give up because help is available.
You can complain, get advice on your consumer rights and be put in contact with trading standards officers who police the rules by going to Consumer Direct .
You can also go to a trade body such as the Retail Motor Industry Federation .