Giovanna Coluccio was none too happy to be tipped with a fruit roll-up.

"We'll hit an ATM later," a 23-year-old guy wearing a button-down and a backpack told her, curiously free of the requisite sheepishness that tipping an attractive woman with a fruit snack should conjure.

Ms. Coluccio, also 23, stayed cool. She smiled, flipped her layered brown hair and walked away, a tray of candy-colored drinks balanced in her arms, a roll of cash tucked in her apron and the roll-up stashed in her pocket.

In her wake, Backpack slurred to his buddy: "I'm gonna marry that girl." The buddy nodded; it was $1 beer night at Turtle Bay, a bar on East 52nd Street.

"Personality is key. Physical looks alone will only get someone so far. Be as friendly, personable, upbeat as possible. Customers will feed off your energy." These are the first rules in a list of best practices, or the shot-girl bible each girl memorizes before she picks up her tray.

For the women like Ms. Coluccio who peddle novelty drinks in Manhattan bars like Turtle Bay, selling shots is a game and a science. Each interaction with a potential customer is an investment, and even an unpromising start usually yields dividends by night's end. (Case in point: Backpack later bought four rounds of shots from Ms. Coluccio. He tipped her $30 in cash.)

Ms. Coluccio is one shot girl in a stable of 25, nearly all of whom are college-educated (though most hold advanced degrees and day jobs). They're managed by former J.P. Morgan and Bear Stearns analysts Bryan Auld and Dominic D'Aleo, who in 2007 co-founded Auld D'Leo Inc., which outsources the services of shot girls to bars in Manhattan.

Having started their company after observing the disorganization and mistreatment of the women, the founders say they saw a business opportunity. Margins are high when attractive women wearing revealing tops and short shorts sell trays of Jell-O shots and watered-down tequila in a plastic test tube. The drinks cost 15 cents to make and sell for $3 or $4.

Messrs. Auld and D'Aleo won't say exactly how much the company makes, but they say profit has increased 16% since 2007 and they're bringing in several hundred thousand dollars a year in profits outsourcing women to sports bars like Turtle Bay, Calico Jacks and McFadden's.

Their product is recession proof. It's all about micro-sales, selling something extremely cheap in mass volume. This is best practice number six: "Do not spend too much time with a patron or group of patrons. The foundation of our strategy relies on high-volume sale propositions. We must walk the fine line of being quantity salesman, while giving respect to those who purchase our items."

The list of 10 best practices of the trade (created by Mr. Auld) is distributed to each woman on her first day of work. The entire stable of ladies meets weekly to discuss and tweak the curriculum of selling practices.

At Turtle Bay, while Ms. Coluccio threaded through the crowds in the bar's upstairs lounge, her co-worker Kristen Peirano, 26, worked the downstairs room, where a televised Yankees game consumed most of the male attention.

"What's the only night of the year no sports are played?" she yelled, sidling up to a group. That got their attention and their business. (Answer: The day after baseball's all-star game.)

Among the other rules in the shot-girl bible: Never give up and always be the friendliest girl in the room. You're not selling cheap liquor, you're selling flirtation.

"For a lot of guys this could be the only time all night a girl comes up and talks to them," Ms. Coluccio said.

Shot girls take home between $300 and $600 a night. They're paid 25 cents for every shot they sell, with the rest coming from tips, which vary between $1 and $20 per round. The very drunk and smitten will drop the odd hundred-dollar bill. After the young woman gets her cut, the cash is evenly split between the bar and the company managers.

Six-hundred dollars a night is a better rate than most women in their 20s can earn, but it's hard work—shot girls must counter rejection with aplomb, continuing to smile and sell to the last.

At the end of a night, Ms. Peirano pulls out all stops. Her secret weapon is her inordinately large hands on a petite and pretty frame.

When a group of guys waver over a round of drinks, she proposes a wager. "If my hands are bigger than yours, you're buying."

They take the bet. They buy the shots.