I'm not a health inspector but I know one...

Lots of stories typically involve mouse droppings, signs of cockroaches, dirty friers/stoves, and improper food storage (like not keeping stuff at proper temp, leaving out condiments, etc).

One place had mouse droppings everywhere and sticky traps with dozens of cockroaches in them. They called in an exterminator to assess the extent of the problem and the exterminator found major cockroach nests behind the walls. He said it was one of the worst infestations he had seen.

At another place, he noticed signs of mouse droppings. Issued them a warning and told them that, next time he came, it'd have to be remedied otherwise they'd face being shut down. He came back a few months later and all was well-- no signs of mice. He goes into their back room and notices that there is a locked closet. He asks them to open it and they say it is unused or something, basically telling him that nobody ever goes in there so he shouldn't either. He says he doesn't care, he has to inspect the entire premises, so they have to open it. Inside, he found a cat's litter box and food dish. They bought a cat to roam the restaurant and catch the mice.

Both places are still open.

The best places? Franchises. They do not mess around with health code violations, as one bad mark can shut down their million dollar businesses.