Long before Ken Starr took on President Bill Clinton in the Whitewater case, he served a less visible — but arguably just as stressful — role.

It was the summer of '66. Starr, a college student, was trekking door to door in the Cincinnati suburbs. His job was to sell Bibles.

Each morning, to psyche himself up for the 12-hour day ahead, he looked in the mirror and said aloud, three times, the mantra drilled into him during training: "I feel healthy. I feel happy. I feel terrific" — even when he didn't feel happy or terrific.

"Luckily, I was healthy during the summer," says Starr, now dean of Pepperdine University's law school.

The company Starr sold books for, Southwestern, is still around (though its main product is now educational study guides). And so, each summer, are the college students.

Southwestern is among a bevy of companies that court students for sales jobs. Each summer — and sometimes into the year — a college-age army nearly 150,000 strong spills out across the nation hawking wares for such companies as Southwestern, Mary Kay, Avon and Cutco Cutlery, a knife-maker. Some go door to door. Many others set up appointments or hold "product parties" to reach customers.

For the companies, the students provide a windfall. They operate as independent contractors, not employees. They pay for all their own gas, food and lodging. They get no automatic health benefits. And they'll do what many others won't: work up to 80 hours a week, usually with no guarantee of pay.

"Young entrepreneurial students have a lot of energy," which is why these jobs can be a good fit, says Joseph Mariano of trade group Direct Selling Association.

Not incidentally, college students are often broke, or close to it. The potential to earn an average 40 percent to 50 percent of a product's price can outweigh the appeal of a minimum-wage job at the college bookstore or a summer internship at a law firm.

Door-to-door sales caught on in the United States in the early 20th century. The practice has waned in recent decades amid a decline in stay-at-home households, evolving state sales rules and rising privacy concerns. Yet, while its demise has been predicted, technology has yet to erase the traveling salesperson's stealth weapon: persuasion. "They can make you feel uncomfortable about saying no or good about saying yes," says Walter Friedman, a Harvard historian who wrote "Birth of a Salesman: The Transformation of Selling in America." "These are the things ads can't do."

How safe are these door-to-door jobs for college students? The industry doesn't keep track of any related crime figures. But direct sales — especially door-to-door knocking — carry the risks involved in selling to strangers in their homes.

Caitlyn Fogerty, 21, is one of about 3,000 college-age students selling Southwestern books this summer. It's a position she seems born for.

In the first four weeks of summer, Fogerty, who'll be a senior at Arizona State University in the fall, has earned more than $16,000. That's twice what the average first-year salesperson makes the entire summer. She earned more than $35,000 in gross profits last summer and close to $24,000 her first year.

On a muggy 80-something-degree June day, Fogerty brushes a strand of chestnut-brown hair off her glistening forehead. She heaves a 30-pound bag onto her shoulder and jogs toward the door of a house in Mountain Brook, Ala., a wealthy suburb of Birmingham that families value for the quality of its schools.

It's 11:40 a.m., and the early promise of the day — she made a sale at the first door she knocked on, at 7:59 a.m. — is waning. No one's home. Five doors in a row. No answer. No chance to give one of 30 daily demos of educational books that help her pay for college.

Selling door to door brings peculiar challenges. Southwestern salespeople will be chased by dogs and yelled at by angry homeowners. Sometimes the police are called if a town restricts soliciting.

But the company, during weeklong training in Nashville before the students scatter across the country, warns them their biggest barrier will be a mental one: overcoming feelings of hopelessness, of self-pity.

"What a young person gains from going out and selling books is how to deal with fear of failure," says Jerry Heffel, Southwestern's president. "That holds people back so much in life. They're afraid to try things because they're afraid they're going to fail at it."

The privately held Nashville company has been recruiting college students to sell books door to door, state by state, since 1868.

Starr says his experience selling Bibles in the 1960s "was unlike anything I had ever done, before or since. It really did require you to run a summer-long marathon and to discipline yourself to stay the course."

Other Southwestern alumni, several in politics, include Texas Gov. Rick Perry, Rep. Marsha Blackburn, R-Tenn., and former Mississippi Gov. Ronnie Musgrove. Blackburn, three decades after selling Southwestern books, occasionally finds herself invoking an adage similar to those she learned way back when. "When you're in the political realm, sometimes people will treat you as if you're an inanimate object," she says. "When that happens, you say to yourself, "I just got another 'no' out of the way, and the next one might be a great big 'yes.' "