Girl Scout cookies available this year include Thin Mint, Savannah Smile, Trefoil, Tagalong, Do-si-do, Samoa and Girl Scout S’mores, the newest variety. (Katherine Frey/The Washington Post)

Girl Scout Sophia Rubeiz says selling Girl Scout cookies is like an art. She should know. The 15-year-old has been at it for nine years.

“When I was younger, I just got relatives to buy cookies,” she says. “Now I have so many customers, and I’m better at selling cookies.”

She has sales goals — and ­strategies. For example, if the inventory of chocolaty, uber-
popular Thin Mints runs out, Sophia doesn’t pass up the opportunity to make a sale. She’ll talk up Do-si-dos, the oatmeal sandwich cookies filled with peanut butter.

“Then people are like, ‘Okay, I’ll try them,’ ” Sophia said.

The high schooler started scouting in kindergarten and sold her first cookies in first grade. Last year, she sold more than 100 boxes in door-to-door sales.

From left, Sirisha Brahmandam, Cristie Samaha, Sophia Rubeiz and Charlie LaPlume of Senior Girl Scout Troop 3438 sell cookies in Fairfax, Virginia, during the 2016 presidential primary. (Jamal Frangie Rubeiz)

Sophia sold more with her troop through table sales outside local grocery stores, restaurants and the Metro station near her home in Fairfax. Last year, she dressed in a Thin Mint costume (made by her mom, the troop leader) to help boost sales.

Girl Scout cookies are fun to sell and fun to eat, Sophia says. (Her favorites are Samoas.) But they also help girls help others. Sophia’s troop decides what to do with the proceeds from each box sold. About half of the money supports local charities and service projects, such as creating goody bags for children at a homeless shelter, buying holiday gifts for children in need and making food kits for kids who might otherwise go hungry. The rest of the money pays for the troop’s activities and trips.

This year marks the 100th anniversary of Girl Scouts selling cookies. In 1917, the Mistletoe Troop in Muskogee, Oklahoma, sold cookies they had baked at home to raise money to send gifts to soldiers in World War I. Other Girl Scout troops loved the idea and followed with their own sales.

Girl Scout cookie sales started small but grew into the largest girl-led business in the United States: Last year’s sales were nearly $800 million, according to the Girl Scouts website.

Lidia Soto-Harmon, head of Girl Scouts Nation’s Capital, says one of the most humbling things about her job is seeing the work that cookie sales enable Girl Scouts to do.

“From welcoming soldiers from overseas back home with cookies at local airports to feeding the homeless to working with animal shelters — it’s like the unseen hand of what the cookie program does.”

Local troops (that includes those in 25 counties in Maryland, Virginia and West Virginia, plus the District) earn about $3 million a year. This year, cookie booth sales start February 17.

Selling cookies has made Sophia a more confident person, she says, and one who can communicate well, deal with rejection and adapt to different situations.

“Most of all, it’s made me excited about trying new things and helping others.”

Cookie fun facts

●The sugar cookie was the first Girl Scout cookie recipe. It was published in the American Girl magazine in 1922, along with sales tips.

●In the 1930s, the selling price for a dozen cookies ranged from 25 cents to 30 cents.

●Last year in the Nation’s Capital region, girls sold almost 4.3 million boxes of cookies and donated more than 134,000 boxes to worthy causes.

●In 2017, the Girl Scouts introduced two new cookies, both called Girl Scout S’mores. Washington-area booths will feature a crunchy graham cracker sandwich with chocolate and marshmallow filling inside. Other parts of the country will have a graham cracker dipped in icing and covered in chocolate.