Secretive deals involving "plant material" often end up badly. And no gardener wants to go to jail, even if they do have a really good horticulture therapy program. The courts show no mercy to us gardeners, maybe it's something about our propensity for digging.
Heck, I remember the time I asked to be excused from jury duty because it was spring. They were not sympathetic or understanding. In fact, I could feel the clerk's eyes rolling, over the phone.
There's a better way to exchange plants without all the risks.( Although I used to know of an underground network pushing that banned perennial, purple loosestrife)
Passalong plants are a win-win proposition, and mostly legal. Passalong plants are traded over back fences between neighbors, tossed at curbs for the quick and the observant, no money necessary. Other times they are traded and sold at garden club plant sales. These specimens can be common as clay soil or rare heirlooms tucked in a babushka and tranported from the motherland. Sometimes the story is actually better than the plant.
Having moved an average of every 2.3 years during my peripatetic life, I've had to leave behind many plants, but the hardest to part with are the passalong plants, the ones with a memory of a person or place. I have managed to maintain a few succulents through the moving; a pussy-toes from my fellow-Californian friend Jody, who now lives in NY, a starfish cactus and a jade plant from propagation class during my first year as a Master Gardener in Kansas, and an unusual stapelia (the latin for that same cactus) from Steph, a new Master Gardener friend. They are some of the plants that I hold dearest.
Stapelia (does anyone know the variety?) The Garden Buzz
Do keep in mind that not every passalong plant is a good thing. A plant described as vigorous may be invasive instead; I'm sure the new owner of my previous garden would like to talk to me about Artemisia "Limelight" and ask me just what I was thinking the day I planted that first sprig. It's not always a bad thing when you say good-bye to a passalong plant. But for the most part they are plants with a proven track record, otherwise they wouldn't be so plentiful for passing along.
(You can read more about all this in Passalong Plants by Steve Bender and Felder Rushing; two garden writers who are equally entertaining and knowledgeable.)