Linda Walker was introduced to "curbstoning" in spring 2003 when a letter arrived at her 95-year-old mother's house in Virginia, informing them that they didn't have a license to run a used-car lot in Southern Maryland.

Walker, 51, sells children's toys, and her mother is retired. They found it disconcerting to learn from zoning officials that 13 used cars were being harbored on a untended sliver of property the family owns along Route 2 in Calvert County.

"Good gosh, we didn't even know [the cars] were there," she said. "They said we would be fined if we didn't remove them."

Walker didn't waste time. She tacked "no trespassing" signs on her property, collected the phone numbers advertised on the cars and called all the potential curbstoners -- a term for those who break the law by selling several used vehicles from the curb without a dealer's license.

"I went on a mission," Walker said. "I asked them all who gave them permission to put their cars there. Everybody said, 'Nobody, it just look like a good place to put a car.' "

Up and down the roadways of Southern Maryland, on front yards and gravel spits, in park-and-rides and vacant lots, the freelance trade of used automobiles is thriving. In one 10-mile span of Route 2/4, the main drag through Calvert County, 26 used cars and trucks were displayed along the margins of the four-lane road one day last month. This count did not include the powerboat, golf cart, flatbed trailer, picnic table, four-wheelers and plowing tools.

"It's simple this way. If someone comes up and wants to drive it, I hand them the keys," said Paul Cocchiaro, 62, a mechanic from Owings who said he has sold a handful of used cars along roadsides in the past several years. "It's different down here in the country; you wouldn't do this in Prince George's County or D.C."

Cocchiaro was asking $1,900 for a 1987 Chevy Silverado he had placed on a friend's property along Route 2/4 last month. It sold within a week. "I've sold other ones in a day, in hours," he said.

To Pat Nutter, a Calvert County zoning enforcement officer, this outdoor commerce is unsightly and dangerous. Calvert is the fastest-growing county in Maryland, and traffic on Route 2/4 is five times as heavy -- 47,700 vehicles a day -- as it was in 1975. Nutter said drivers frequently stop in turn lanes or on the shoulder to check out used cars for sale, creating traffic hazards.

As Southern Maryland develops, curbstoning also increasingly collides with the aesthetic sensibilities of modern suburbia. "We're constantly getting complaints," Nutter said. "It looks like a multitude of used-car lots as you're coming down the road."

Nutter said he has no problem with the person who chooses to park his own vehicle on his own property to try to find a good deal on a quick sell. But along with state and other Southern Maryland authorities, he is trying to crack down on the businessman who buys cheap cars, often at auction, and resells them along roads without paying taxes, owning a dealer's license or putting the cars through state inspections.

A Maryland Vehicle Administration study from the early 1980s found that the state loses $8.75 million in excise taxes from unlicensed car sales. George N. Manis, executive director of the Maryland Delaware Independent Automobile Dealers Association, estimates that figure is three or four times as higher today.

Curbstoning has become enough of a concern that two years ago Maryland enacted legislation decreasing from four to two the number of cars an individual may sell in one year without a license and raising the maximum fine from $1,000 to $5,000. In December, a task force was established of state transportation officials and officials from the Southern Maryland counties -- Calvert, Charles and St. Mary's -- to coordinate their response to unlicensed car dealers.

"Southern Maryland has become another hot spot right now," said Andy Srebroski, a manager in the investigations division of the Maryland Motor Vehicle Administration. "We're really on an upturn as far as writing a lot of citations for this."

Two years ago, three cases of curbstoning went to court in Maryland, Srebroski said. So far this year, 18 illegal used-car salesmen have been prosecuted. In Charles County, zoning officers received 1,264 complaints last year about untagged vehicles littering roadways and people's yards -- more than 20 percent of all zoning complaints.

In Virginia, the Independent Automobile Dealers Association is starting a campaign to focus government attention on the pervasiveness of curbstoning and the fact that it drains money from the state because taxes are not collected. "This is a nationwide problem," said Lois Keenan, the association's executive director. "It seems to be just everywhere you turn -- not just business parking lots but private property, particularly along main thoroughfares."

But those who choose to sell their vehicles themselves say there are some advantages to this method. The landscape is tailored to it, for one; Southern Maryland roads are congested with potential buyers, but they often pass through fields or widely spaced developments where there's room to show off the merchandise. In addition, there's none of the hard bargaining with a used-car dealer. And for the sellers, profits aren't sliced away by selling on the Internet, they say.

Bruce Bridgett, 22, a volunteer firefighter from Hughesville, bought his white Pontiac Trans Am on eBay four years ago but chose to display it on his friend's front lawn along Route 5 in Charles County when it was time to sell. Price tag: $18,500. "It's a 25th anniversary limited edition," he said. "I want to get the money it's worth. And you're not going to get as much from a dealer as you could selling it yourself."

There can be hassles with selling one's own vehicle. Frank Hall, 38, a diesel mechanic who lives near Prince Frederick, sold his Wave Runner from his lawn along Route 231 within 10 days in July -- but not before thieves ripped off the tags that make it water-legal. The same thing happened to a car he sold a few years earlier.

It still beats the alternative, he said. "I would never advertise anymore. My number one choice is to eliminate the middle man."

Licensed used-car dealers say individual sellers, especially unauthorized dealers, not only siphon off their business but can also pose a risk to consumers. There is no regulation of the condition of the vehicles, increasing the chances of getting a jalopy without a warranty that breaks down shortly after the sale, or ending up with an odometer that has been turned back, said Tom Hodges, owner of Tom Hodges Auto Sales in St. Mary's County.

"I've had many persons say, 'God, I wish I'd never bought that car, it's mechanically in bad shape,' " he said. Hodges estimated that unlicensed dealer sales account for more than half of the cars sold on the streets in Southern Maryland.

"It would be no problem if there were a few cars in people's yards that they need to sell, but that's not what's happening," he said. "It's the road bandits that are doing it. It's a pretty easy hustle to pull."

Waldorf residents, from left, Donnie Diamond and Kevin Fort stop along Route 5 in Hughesville to look at Bruce Bridgett's Trans Am. On his property on Route 231 in Prince Frederick, Rob Moorehead displays a friend's Camaro and a relative's truck for traveling shoppers to see.