When I was in Mexico, the base state of being in business is a tray of food around your neck with a heat source. Somebody had practically every corner covered. My hosts had their favorites and I ate everything from fish to beef with no ill effects. True, you were, in my opinion, taking your chances. But the vendors seemed to have tasty and hot food. (The spices and heat probably cuts down on bacteria.)
If Mexico had the laws and regulation we have here none of those people would be making a living. What we need here is fewer laws and regulation.
They also operate here with no regulation: no business license, no sanitation certificate, etc., because illegals are a "protected" class.