On the Nile cruise ships, when the ship stops to go through the locks at Edfu, vendors gather in small brightly painted boats on the river below to hawk their wares (scarves, shawls, gallebejas, etc.).
You bargain from the upper deck of the boat, they throw the merchandise in a plastic bag up to the buyer, and you throw back the sack with the agreed sum in it.
Much haggling goes on and amazingly, little merchandise or money ends up in the water.
The vendors are very adept at retrieving either in the event of a mishap !