At checkout, she types in the addresses the couriers provide in their home countries. When they land in Dakar, they call her cellphone and arrange to meet so that she can collect her purchases.

“You don’t give your stuff to any G.P.,” Ms. Seck said, adding that she asked for references and checked online reviews. “They will say, ‘O.K., she is good,’ or ‘She comes late’. If it’s a tardiness issue, that’s O.K. But a trust issue? I won’t use her.”

Alioune Sine’s sister has been delivering American goods to Senegalese clients for two decades. Mr. Sine, 44, a filmmaker who helps with his sister’s business, said that they had gotten busier with the rise of e-commerce and recruit friends and cousins to help transport more suitcases.

G.P.s often operate on slim profit margins. They hunt for low-priced tickets: Up to $1,300 is viewed as acceptable for a round-trip flight from New York to Senegal. But to retain customers, many of the couriers continue to fly even when prices spike during the holidays, and the economic math becomes precarious.

Airlines typically allow an international passenger to check two pieces of luggage with a ticket. On a Delta Air Lines flight to West Africa, for example, it costs $200 for each extra piece of baggage weighing up to 70 pounds.

On Delta, Mr. Sine said, his family company’s shippers take the maximum number of bags: 10.

“When we get to the airport, we get one big hand truck, and it’s back and forth, back and forth,” Mr. Sine said on a recent morning at a barbershop in Harlem where the company rents an office. He was sorting through bundles of brightly colored African clothing, calling the phone numbers of customers written on each, telling them to come pick up their packages.

G.P.s tend to carry fewer bags, and make less money, on return trips, when they carry mostly lighter items like custom traditional boubou dresses.