I was in such a market a year ago in Kowloon- across the water from Hong Kong. I had to go outside as the combination of the smell and other things (like the machine they put chickens in right after they wring their necks that pulls out all their feathers) was making me sick. I feel nauseous just remembering it. ugh.
Oy, Not to mention that lavatories in rural China consist of a hole in the ground.
Still, not as bad as San Francisco.