If you're lucky, they'll not do business with you. If they're clever, they will do business with you, and then report you to the guards. Sometimes they'll just skip straight to the latter. Flogging loot from an adventure is one thing, but most adventure shop buyers expect things like weapons, armor, and occasionally maybe valuable crafts and silverware. Come in with ten units of beaver hide and thirty units of ceder wood, and they're going to wonder what caravan just got hit.