You can trust me, honest

"My name is Martin and I used to be a second- hand car dealer." How I long to stand up in a room of fellow sinners and bare my soul in mutual confession. But no, while alcoholics, drug addicts and sexual deviants are all admirably catered for by well-meaning liberals, those of us most in need of reconstructive therapy are left to fend for ourselves and shunned by society.

In my late teens I bought and sold bargain-basement classics - MGs, Triumphs, Alfas - tarted up and flogged on quick for up to pounds 2,000 profit. An MG Midget that should have been put out of its misery would be bought for as little as pounds 300, I'd replace the interior for about pounds 100, get it filled and painted for pounds 400 and sell it to some fool for three grand. I had no qualms then about disguising cavernous rust holes and the tell-tale signs of mistreatment, and lying through my teeth about provenance, anything to shift the damn things. I parked cars on uneven driveways to hide collapsing suspensions, stuffed sills with newspaper and glued carpets over holes in the floor.

Of course, there are used-car traders who never question the morality of such methods, men for whom guilt is something used to make furniture pretty and shame a Wild West hero. Men (they are exclusively men) who will stop at nothing to move rusting hulks of unloved metal from their forecourts and onto the drives of simple folk untutored in the depths of human depravity.

Men like Steve. When it comes to the tricks of the trade Steve is Paul Daniels. If you want to know how to make an easy pounds 2,000 a month for next to no effort and modest outlay, he's your man: "Very thick oil in the engine is a good one to stop smoke long enough for a test drive, some swear by black treacle." He laughs heartily at this. "I cover filler with tin foil or use metal-based filler so that anyone with a magnet won't find it. They've all read the guide books and think they're on to a winner if the car has good pedal rubbers, so I put new ones on. In the old days I've even known people to use half a dozen eggs in the radiator to stop a leak, just long enough to get the car through the auction. Most buyers haven't got a clue what they're doing and spend five minutes looking at the car and another five driving it. Often, if they've got the money, like the colour, and the stereo's OK, it's a sale."

Steve's forecourt, on waste ground next to a station, is an almost precise replica of Frank Butcher's in EastEnders, with strings of triangular flags spreading like the spiky fronds of a Venus flytrap from a freshly whitewashed Portacabin. He has bought and sold second-hand motors for 20 years. How has he been so successful?

Firstly, he has one significant advantage over you or I, he can get to cars before we even know they are for sale. He has a mole at the local paper. For pounds 10 a week they let him know what cars are for sale a day before the advertisements appear. Ever rung up to enquire about a car on the morning the advert appeared, only to find it has already been sold? That'll be Steve, or an equally nefarious trader. In London, most dealers know that you can get the Autotrader, which normally comes out locally on a Thursday, from newsagents in Kings Cross on a Wednesday night.

Most stock is acquired through part-exchange though - they can pick up a customer's old car for the proverbial snip. "You can tell it in their faces," says Steve. "They're looking at the car they want to buy and that's all they can think about. Some of them would take a box of Smarties if I offered it."

I thought it would be interesting to take my car, worth about pounds 2,000, to a few garages to see what I'd be offered for it in part-exchange, and what delights they'd try and sell me to replace it. Like shoe shops, independent used-car traders tend to stick together. My nearest Portacabin shanty town has five car lots and, like Steve's, they are all festooned with strings of triangular flags, a semaphore warning to the unwise: "Sharks Feeding."

I was offered between pounds 700 and "a thou" for the car (a Volkswagen), by the five dealers I approached (one of them was selling an almost identical car for pounds 2,200). Only one was straight with me, he advised me to sell it privately. Nearly all of his cars, I noticed, had little Law Data stickers over the mileometers, informing buyers that the car's mileages could not be authenticated so should not be assumed genuine. He told me this was a legal requirement if cars had no history, but none of the other traders I visited used them, even on cars which had no service records.

One of them, a greying, stout man in his late fifties whose yard was graced by tatty Golfs and Escorts, was typically evasive when I asked about the history of a D-reg Golf with 54,000 miles on the clock, but the body of an octogenarian. He treated me to a well-rehearsed charade in which he has mislaid the service history, searches his desk and then asks various salesmen and mechanics if they have seen it. He had it somewhere, he assured me, he'd dig it out later; would I like a test drive? I could literally smell the filler in the air from the workshop behind his sales office, decorated with fake teak walls, brown shagpile and grotesque needlepoint landscapes.

I wondered aloud about a dejected H-reg Nissan in the corner. "It's having a gearbox, it went the other day." A new gearbox, I asked? "Another gearbox," he replied vaguely. He started up a red, F-reg Escort nearby. At idle its engine complained chronically, like a distressed convict rattling his spoon across the bars of a cell, but I was more interested in its paintwork. It was thick, shiny, vivid-red gloss which, judging by the sloppy overspray on the window rubbers and chrome, had been applied by a bargain-basement amateur. It almost certainly hid severe accident damage or rust, but to Joe Punter it would look a dream. Thus, a car that Laurel and Hardy would have rejected as an embarrassing eyesore when it first arrived was, through nothing short of alchemy, now sitting here as "Bargain of the Week".

Noel Lee is such dealers' worst enemy, Dirty Harry with a spanner. He has been a vehicle inspector for the AA for 24 years. According to him, it's not just cheap canines that you need to be wary of: "A few years ago a customer asked me to look at an Aston Martin he'd bought a couple of years earlier as an investment. He'd already lost about pounds 40,000. Then, when I started to check it over, I found the inner wheel arches were stuffed with copies of the Manchester Evening News and covered over with Heinz baked beans cans."

Professional inspections are the best way of unearthing money pits, but they can cost more than pounds 150, and you may have to wait for six days. Any car still for sale then, especially privately, is unlikely to be a bargain and, if you are looking at cars under pounds 2,000, inspections soon become financially unviable. Far better, if possible, is to take the car for an MOT test; for pounds 25 you'll discover if it is safe, if it's been involved in a serious accident or, worse, if it's two cars welded together (a "cut and shut"). However, if you are looking at several cars, which is advisable, even MOTs become expensive. Ultimately, it will come down to you against them, but before you can suss out the rogue cars, you have to spot the rogue dealers.

Not as easy as it sounds, according to Trading Standards officer Frank Smith: "There are a lot of traders working from home to avoid the Trades Description Act. Anyone can be a motor trader in England, you don't need a licence, so it's easy to pretend to be a private seller. It is against the Fair Trading Act though and we monitor newspapers and log telephone numbers but it is an impossible task to keep track of them all."

Prosecutions of covert dealers are rare but they are fairly easy to spot. I picked up my local paper on the way home and saw this suspicious ad: Alfa Romeo 164 3.0 V6, Manual, H-reg, Alfa red, full electric pack, c/locking, abs, sunroof, one previous owner, long MOT, pounds 4,765. It gave a mobile-phone number. A dealer I reckoned as the ad is laden with jargon. Instead of a year of manufacture it gives a registration letter which probably means it is an early H; the subject of mileage is avoided, likewise the service history - both essentials - while less important extras are emphasised. Does "one previous owner" include the current vendor? If he isn't registered as the second owner of the car, why not? The mobile number is the final give-away though, so I rang it and asked about "the car" rather than "the 164". The vendor had to ask me "which car?" I asked him outright if he was a dealer. No, he said he wasn't, but was selling the other car for "a friend". Very likely.

Unfortunately the old cliche about paying money and taking choices is never more appropriate than in the used car market. Respectable dealers will ask up to 40 per cent more than a private seller for the same car, but they provide the comfort of consumer legislation. The dealers mentioned above simply aren't worth bothering with. Their forecourt prices will be lower but almost all of the cars I saw were howling like wolves. And don't expect them to be Claire Rayner when something goes wrong and you want a refund.

Ideally, it's best to buy a used car from a franchised main dealer whose cars will have genuine histories, are checked thoroughly and come with a warranty. Unless you know that a local independent dealer is the salt of the earth and has been around for years, steer clear. Finally, when the salesman (in shiny suit or scruffy tracksuit), dangles the keys to one of his fleet, you could do worse than ask yourself one simple, famous question: Would I buy a used car from this man? !