Morally, morals don't have much to do with this.

Practically, it's impossible for me to judge the sanitary conditions of a food stall. Or, if possible, it'd be wasteful for everyone to spend two hours checking everything instead of, as a society, organising a system where a trained professional does that for all of us.

Specifically, you would need to carry a thermometer to check both the refrigeration as well as hot storage. You'd want to take samples and send them to a lab for bacterial cultures. You need to check the employees' bathroom for soap and clean towels. Then, come back the next morning and check that they threw out leftovers that can't be kept overnight, and properly sealed and stored those that can. Make sure people, especially doctors, know your toll-free number to report incidents of food poisoning that may be linked to restaurants.