We don't lack regulations, what we DO lack is application and enforcement in VietNam.
Ha Noi, as a larger city, has a lot of dubious quality street food, especially featuring CHOLERA, due often to the poor quality water sources used by food vendors. It seems that the Health Department there only gets active when complaints come in.
Ho Chi Minh City on the other hand is very, very proactive. Their Health Department goes out looking for trouble. Witness the number of restaurants closed by them, often with a Cong An posted outside their door to enforce closure.
The HCM Health Department also takes food samples from vendors and tests them. They also check food imports coming in to the SaiGon Port. They had a well publicised stand-off with a meat importer a couple of years ago where some dubious meat arrived on a reefer (frozen food ship) and was impounded right at the docks. Stayed there for months under impound. Then, one night, the electrical power 'failed' and they turned into a smelly mess which allowed the city to order them to be removed.
The CGST often stop vehicles travelling overnight to see if there is food on board. Live fowl, and eggs, carried by motorcycles are also their targets. Remember, eggs have to be clearly stamped - not just a felt tip pen mark!
Your best protection, when eating at a street vendors, is YOU. Busy vendors, with line-ups (queues) exhibit two things: busy (fast food turn over) and line-ups (good reputation).
The problem, though, is water. Do they have a running water supply or does it come from containers? Is the dish-washing water clear and soapy, or greasy and clouded?
I buy Banh Me buns from a store in the Tan My area of Quan 7. On one occasion a server/preparer had been attending her personal hygiene and, without washing her hands, made to get my buns. I said NO, forget it. The owner, who spoke English, asked why, and I explained I like people with clean hands. They wear plastic food gloves now.
Hand-washing is not common. a survey a few years ago of foodworkers and wait staff revealed 94% did NOT wash their hands after attending the toilet!
Nhu Lan Restaurant and Bakery (get your moon cakes NOW!) on Ham Nhi has excellent cleanliness - they also have a meat factory on Hai Ba Trung near Vo Thi Sau. Their waitresses, if asked for recommendations, will often guide you to the freshest dishes, although most are made daily.
In a supermarket, older women are usually your best guide for the best foods. Vietnamese shoppers must be some of the 'Best Before' readers in the world.
Remember, certain foods are cooked in such a way they don't degrade. Chinese-style barbecue meats have a proven long, unrefrigerated, life as do certain Vietnamese dishes.
But food crooks exist. Look at the ends of stalks of Durian (my favourite) and Jackfruit - if there are any holes (usually three) in the stalk, the chances are they have been injected with Chinese food life extenders.
If street coffee costs less than 20-30 Dong a cup, the chances are it is fake made from soy powder and Chinese chemicals. The TP HCM Health Department roots these things out and closes places where they are made.