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Some insurers promise cheap car-insurance rates even if you have a string of speeding tickets or bad credit.

How can they do it?

The answers are in the fine print of their car-insurance policies. Behind a seemingly great bargain could lurk a series of exclusions and limits that reduce the likelihood you can file a claim.

But you can't tell solely by the price they charge. Shopping for affordable insurance isn't like shopping for cheap gas. One insurance company's quote could exclude coverage that another might include at the same price.

"It's OK to compare prices, but once you see the prices, you have to find out what's covered and what's not covered and make sure you're comparing apples to apples," says Penny Gusner, a CarInsurance.com consumer analyst.

If you're a low-mileage driver, you might want to look first at what are known as "pay-as-you-drive" plans and consider other common types of car-insurance discounts. If none of those seems like a good fit, here's what to watch out for as you explore other options.

7 fine-print gotchas

Preferred or standard car-insurance policies are geared to drivers with clean or moderately clean driving records and decent credit ratings. Nonstandard policies are designed for risky customers who don't qualify for standard or preferred rates. Some are written specifically for specialty cars, such as a Ferrari or a restored '57 Chevy.

Smaller companies that specialize in catering to high-risk customers or classic-car owners used to dominate the nonstandard market. But today, many major insurers, such as Allstate and State Farm, sell both standard and nonstandard policies.

With nonstandard car insurance accounting for about a fifth of the private passenger auto insurance market, according to industry analyst Conning & Co., it's easy to see why insurers want a piece of the action. But no insurance company is going to take on extra risk without offsetting it, either by charging higher rates, reducing coverage or both.

Here are seven surprises that might be hiding in cheap, nonstandard policies:

No. 1: No coverage, or reduced coverage, for some drivers

Generally a standard policy covers you, the listed members of your household and friends or relatives you let borrow the car occasionally.

But if you have a risky driver living with you -- a teenage boy with a speeding ticket, for instance -- a nonstandard policy might require you to exclude him from coverage.

Some nonstandard policies also exclude coverage for “permissive” drivers -- people who use your car occasionally with your permission. Or they might exclude coverage for permissive drivers under age 25 or 21.

In some states, insurers can include step-down provisions in their policies. Under a step-down provision, the liability limits are reduced to state required minimum levels when someone who's not named on the policy drives your car. So even if you pay for higher-than-required liability coverage, you could have less protection when you let a friend borrow your car than when you're driving.

No. 2: More driving-record checks

"If you're a preferred driver, an insurance company may check your driving record once a year or maybe once every other year," Gusner says.

But if you already have a checkered driving history, the insurer might check your driving record every six months, before each coverage term begins, so it can adjust the premium accordingly.

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