1. Street Vendor Meat
The issue with meat products from street vendors has to do with how long the food has been exposed to air and sun. Hours-old meat is likely to have been contaminated by insects, not to mention started down the line toward spoilage. You may also have no idea how carefully the food was stored prior to cooking.
However, if that taco stand is hopping with customers, both local and tourist, you know that the turnover is quick and that the food being prepared fresh, not sitting around all day. In this case, it’s probably safe to partake in the cuisine.