> Really? At least here (Canada), you absolutely do need food safe certifications to sell any food at farmers markets.

Sure, but you still have many more human hands on your head of lettuce on a farmers market (plus all the contamination from potential buyers sneezing, grabbing produce to check it out or from the environment in general aka flying birds, mice, rats, ...) than there will be on the mass produced lettuce that maybe saw a human hand at picking and everything since then is automated.

IIRC outbreaks in mass-produced green stuff usually end up tied to farmers or their neighbors spraying fecal based fertilizer at the wrong time. Unfortunately... that makes the blast radius of such a thing much, much worse.