Each seller has a boat filled with food, wood carvings, t-shirts, or a variety of other tourist focused items.  As our boat was paddled through the markets, we constantly collided with others boats, were (literally) hooked and pulled in by keen sellers and rocked side to side by the wake of long boats travelling down the same canals.  Whilst I do not think the boats roll over very often it did not feel completely safe, particularly when we had to rearrange our seating order because the weight of the passengers was causing one edge of the boat to ride dangerously low to the water.