For a dealer, Bray said, a lost shipment is just part of the cost of doing business. He said the couple needn't worry about some nefarious character showing up at their door, looking for his merchandise.

Bray explained the economics:

When undercover officers make wholesale buys, usually they pay about $1,000 a pound for medium-grade marijuana. So the 33 pounds that Anderson and Sloan received probably cost the local importer about $33,000. As a rule of thumb, a pound can be stretched into 360 $10 bags, meaning the shipment's retail value was nearly $120,000.

That's a profit of $87,000 or so. Multiply that by, say, five shipments, and the overall profit is north of $400,000. If you lose one of the five packages, so what? You're still roughly $300,000 in the black.

"Therein lies the reason why it continues to occur on a frequent basis," Bray said, adding that D.C. police recover 30 to 40 such shipments a year. "And it's very difficult to trace these packages to the people who sent them," he said. The box shipped to Anderson and Sloan had a return address in Anaheim, Calif., that apparently is fictitious.

Perhaps the most memorable recovery in the Washington area occurred July 29, 2008, when heavily armed police officers who had been tracking a marijuana shipment to Prince George's County raided the home of the unwitting recipients, Berwyn Heights Mayor Cheye Calvo and his wife, Trinity Tomsic. In the chaos, officers shot and killed the couple's two black Labrador retrievers.

Sloan and Anderson have a German shepherd named Cheyenne. Sloan said the Berwyn Heights fiasco sprang to her mind the instant her husband told her about the coffee grounds.

"Before he even looked in to see what kind of drugs they were, I called 911," she said. "I told them exactly what was going on. I'm like, I don't want them coming through my door with guns drawn, because I love my dog."