In SoCal, they are very inventive ... they get used or cheap Mtn Bikes and modify them for use as cargo bikes. The frame is welded up from 1/2" square tubing ... with two 26" front tires. The cargo box is welded to the front fork in 2 places and welded to the handlebars as well. They don't usually carry more than 50 - 100 lbs. (max 50 Kg).
The box sits up high for easy vending. They vend fruits, peanuts, cotton candy and various other items throughout the Spanish neighborhoods.
I had hoped to get a foto of one of these ... and two of them showed up this morning at Jack's bikeshop. By means of a little English (one of them), a little Spanish (me), and some sign language ... I helped Jack figure out what they wanted. Basically one trike needed the rear brake pads replaced and the brake cable fixed. Maybe I should get together with my neighbors and find out what the Spanish words are for the various parts and conditions of the bicycle. That might help Jack and I in the future.