This year, it's not just the turkeys that are getting worried as we get closer to Christmas - used car dealers are having a tough time. Some who are used to selling a car a day are failing to sell one a week, and prices at car auctions are falling as a result. November/December was always a good time to buy a car at auction, but this year you'll find some of the prices impossible to resist.

What can you expect?

If you are looking for cheap, reliable, comfortable motoring, you cannot beat the post-1997 (R plate and onwards) Ford Mondeo. These cars are very good to drive, cheap to fix and insure, and often come with an airbag and air conditioning. If you can get past the image problem, these cars are spectacular bargains at auction.

Earlier this year, What Car voted the 1.8LX model the best used car purchase. Two or three-year-old cars with 80,000-100,000 miles on the clock can be bought week in, week out for around £2,000 - considerably less if they are in an unpopular colour or have the odd scrape.

Last week, at the British Car Auction's site at Blackbushe in Surrey, the next model up - a 97,000 mile, 1999V Mondeo 2.0GLX - sold for £2,325. Virtually the same car at the Great Trade Centre car supermarket in London will cost you £3,600.

If you've been put off by the high mileages of these cars, don't be. Young rep-mobiles that have clocked up big distances at 80mph on motorways are almost always in better mechanical condition than lower mileage cars that have been driven around town.

The advantage you have in purchasing such a car is that it's lost most of its depreciation already. That GLX will probably run for another four years or 50,000 miles of family use without too much needing to be spent on it - apart from a £500 clutch. At the end of the four years you could give it away and still have only lost £500-£600 a year in depreciation.

Younger cars

If you've got a bit more to spend, there are plenty of other bargains. At the same BCA sale, four 2001 Toyota Avensis GS with the excellent D-4D diesel engine and 13,000-32,000 miles on the clock sold for between £7,250 and £7,850. Two-year-old Citroen Xsara Picasso 1.6SXs with 14,000 to 22,000 miles were £6,000-£6,700.

Ford Focuses are now cheap, and new shape Mondeos are starting to appear for two-thirds of their price new. One-year-old Fiesta 1.25 Freestyles with power-assisted steering, a CD player, and around 15,000 miles now sell for around £4,500 and Micras of a similar age make just £3,300.

Now's a good time to buy convertibles - a 65,000 99T Audi Cabrio 1.8 sold for £9,000; other low bids included £6,450 for a 81,000 mile 99T Mercedes C240 Esprit auto.

Caveat emptor

Auctions are not for everyone. To be successful, you have to go with an open mind. If you are in the market for the sort of cars that fleets are made of, you will have plenty to choose from. Trying to buy clean estate cars is difficult, unless you've got plenty to spend (£7,000+) or you're happy with an Astra. If you want a luxury car or 4x4, there are sales that specialise in those areas.

Unless you really know your vehicles, you should probably stick to ex-fleet cars that come with a warranted mileage and a service history. The biggest problem with the actual sale is you don't get a lot of time to examine the inside of the car. When you arrive they will be parked in long rows, usually under cover. Each car is dri ven through the sales hall and you want to be present as soon as it's unlocked and started. If it has air-con, turn it on and make sure it runs cold. Open the boot to look at its condition and examine the spare tyre. If it's an estate, look at the roof for evidence of hauling heavy loads.

Have the back seats been used? Look in the ashtray, examine the seats for burns and condition. Listen to the exhaust and clutch, and check the tyres for even wear. After you've looked at a few cars you'll soon be able to spot the better ones.

Decide on your top price and find a good place to stand. Let the dealers take it up to their bidding and come in as late as you dare. Never go over your price. If you think the auctioneer is running you up, shake your head and walk away.

If you're successful, try not to punch the air in triumph but instead move to the rostrum where you will be required to pay a 10% or £500 deposit with cash or Switch.

If the car is "sold provisionally", this means the auctioneer will phone the vendor to see if they will accept the hammer price - a long wait can ensue. The balance (including a 1.5%-2% buyers' premium) is payable before you collect the car. You have one hour from the end of the sale to complain (in person) if you feel the car is not as described in the catalogue.

One other problem is getting it home. Most cars don't have a tax disc so it's probably best to get the auction company to deliver it at a cost of £40-£50.

There's nothing more exciting than buying a car at auction - especially when you know the money you're saving will pay for next year's holiday.

· Car auctions: www.bca-auctions.co.uk

Buying advice: www.honestjohn.co.uk

Used car values: www.whatcar.com or the Great Trade Centre: www.gtccar.co.uk