The conventional wisdom holds that smart consumers shop around and wind up saving money.

And you know what? The conventional wisdom is right -- big time -- at least when it comes to car insurance.

Washington Consumers' Checkbook, a local magazine that surveys goods and services around here, comparison-shopped at more than a dozen insurance carriers active in the Washington area, presenting them with four combinations of cars and drivers, and found very large differences in the prices quoted for drivers in exactly the same situation.

In some cases, the highest price quoted was quadruple the lowest.

"It's quite amazing how big the differences are," said Robert Krughoff, president of the Center for the Study of Services, which publishes Checkbook. "There's real money involved here."

The differences are much greater than they were in Checkbook's last survey in the early 1990s, he added, so savings that were a few hundred dollars then can be $1,000 to $2,000 now. Also, he said, in the past the companies with very high rates tended to be minor players in the Washington market. Now "we find companies that are very large players in the market, with hundreds of thousands of policyholders, have very high rates."

The magazine looked at prices for the following people, all with clean driving records and excellent credit ratings:

* A married couple, ages 34 and 35, homeowners, driving a 2001 Ford Taurus (15,000 miles annually) and a 1998 Toyota Corolla (12,000 miles).

* A married couple, ages 61 and 62, homeowners, with a 19-year-old daughter, a college student, living at home, same cars as above (12,000 and 6,000 miles).

* A single woman, age 30, driving a 2002 Toyota Camry (10,000 miles).

* A senior citizen, age 65, retired, driving a 2000 Buick Regal (pleasure only).

It sought prices for these drivers in the District (postal Zip code 20008), Montgomery County (20814), Prince George's (20740), Arlington (22203) and Fairfax (22030). Rates were for a fairly standard coverage package, though there were some variations between the jurisdictions because of differing regulation.

Differences of $1,000 or more were common for the couples in the District and Maryland, and more than $500 in Virginia. The two single drivers generally had lower rates, but not always, so variations were not as large. However, in some jurisdictions they were still startling -- the lowest rate for the senior citizen in Arlington was $480 from Geico and the highest was $1,008 from Progressive.

Insurers say many factors go into their prices, including their experience with claims in a jurisdiction; their reading of the regulatory and litigation climate there; and business goals, such as a desire to build market share or an effort to trim business in an area to reduce exposure to big storms or other disasters.

"Every single company believes that they have hit upon the exact ingredients for the perfect secret sauce, [the formula] that matches risk and cost perfectly," said Julie Rochman of the American Insurance Association, a trade group of property insurers. "Each believes it about themselves, and thinks others are getting it wrong."

J. Robert Hunter, director of insurance for the Consumer Federation of America, said the secret is that most drivers don't shop, and insurers know it.

"It's not a very competitive business. . . . Turnover [among policyholders] is very slow. There's huge inertia," he said.

Hunter said fear also plays a role. People worry they may buy the wrong coverage or get canceled. They may have been with their current carrier for years, and they think, "So I save $50 or $100 -- what if I have an accident the first year?" he said.

Insurance also involves very complex legal documents, and motorists "are not sure what they are buying. . . . There's a strange combination of fear and boredom," Hunter added.

The Checkbook report, which appears in its spring/summer issue, notes that the Internet has made it easier to shop for insurance. Independent Web sites and the companies' own sites allow consumers to make at least rough comparisons, and "even if you have to request quotes by phone from companies and agents, the effort is small compared to the potential year-after-year savings."

Hunter agreed. "The tools are there," he said. Many states' insurance regulators offer shopping guides, some containing representative rates for areas within the state.

Krughoff acknowledged that shopping requires some effort but agrees the payoff can be well worth it. "Most people don't get paid $1,000 for 15 minutes' work," he said. But he also cautioned that with rates changing as they have been, consumers would be wise to check again in a couple of years to see if their rates are still competitive.

Krughoff and Hunter both noted an indirect benefit of shopping as well. If large numbers of consumers start shopping, that will put pressure on the high-cost carriers. If consumers shopped vigorously, "the companies with high rates would be losing all their customers," Krughoff said.

It's also a good time to review your coverage itself. You may well be able to save additional dollars by better tailoring your policy to your situation. Could you afford to pay $1,000 in repairs yourself? Consider raising the deductible on your collision coverage. Or maybe the car isn't worth $1,000 anymore. In that case you might drop collision altogether.

Insurers say they have found a very clear correlation between good credit and lower accident rates, so if you have a great credit rating, be sure the carrier knows. Pulling credit reports when pricing a potential customer's insurance is highly controversial, and some states, including Maryland, forbid it. The District and Virginia allow insurers to factor credit ratings in to their prices.

The impact of credit can be substantial. Checkbook found a difference of $1,088 in the District and $536 in Virginia between the rate a carrier quoted for an "average" credit rating and the rate quoted when the company was able to check a real Social Security number and found the person had excellent credit.

Attention, high rollers: An Internal Revenue Service deadline looms for those who tried to cut taxes using the "Son of Boss" shelter. They have until June 21 to come in and 'fess up. Otherwise, the agency, which has obtained lists of participants from law and accounting firms, says it's sending out a posse.