Did you know that having and operating a car eats up 10 to 20 per cent of your revenue? You will realize that a car is one of the biggest buys you will ever make. Therefore, it is well to shop carefully, and to refuse to take what doesn't suit you in every respect. Perhaps the first question you ask yourself when you go to buy a car is: "Should it be new or used?" There are advantages and disadvantages to each.

Used car salesmen like any other group of businessmen range from responsible to crooked. But even the best of them make their money by selling you on a used car fast. So keep your wits about you while listening to a sales talk, and don't be pressured into a quick decision.

One advantage of a used car has to do with depreciation. It's a sad fact that the value of a new car diminishes drastically in its very first year, no matter what kind of treatment you give it. In reality, the minute you drive a car out of the showroom, it becomes "used", and is worth 30 to 40 per cent less than the total on the sales slip you got ten minutes before. This drop in value is what is called depreciation. If you buy a used car, it is the previous owner who suffers the sharp first-year loss in its value.

In addition to savings on depreciation, the greatest single advantage of a used car is, of course, the lower initial cost. On the debit side, however, repairs are usually needed more frequently, and guarantees and warranties are more limited than for new cars.

Used cars are not necessarily bargains on another count. They may have major weaknesses from having been driven hard and maintained badly. Yet such weaknesses can be concealed beneath a gleaming exterior of new paint or wax. Therefore, when you find a used car you like, you should have a mechanic examine it thoroughly before you make a final decision to buy it. If you have a regular mechanic and are a good customer, he may check over one or two cars free. Otherwise, you will probably have to pay a flat fee for a mechanic's service, which is well worth it.

If you don't know a mechanic whose judgment you trust, you should try to find an computerized diagnostic workshop. They will check potential trouble spots in a car. The best of these car workshops are the ones that do checkups only, without operating a repair service of their own. After you know the condition of the car, now you can decide there are more minuses than pluses in buying a used car. That brings you to a new car.

Take a critical, careful look at the car outside and in, and then go home to think about it before you decide. Remember that although each used car is, by definition, unique, people trade cars in every day, and if you miss one treasure, you will almost certainly find another next week.