There is a little divey eatery in SF that I go to quite often. Dust is embedded in the grease on the hood over the stove, the windows and floor are filthy. But the grill is clean and I've never gotten anything close to a stomach problem from the place. One of the benefits to the rather disgusting look of the place is that people walk in, look and walk out. It keeps seats open for those of us who are regulars!