Not a slam on the vendors but:
Most of the flea market vendors are carrying around the same "stuff" that they started with years ago. Some is so shop worn that its pretty useless.
The tool vendors? Where do they find tools that are even cheaper made than those at Harbor Freight? Some is really junk.
Vitamin pill peddlers? Where do they get this stuff? Is it safe? Is there an outside chance that it will be of at least the same value to medicine as an aspirin?
But: We continue to walk down the isles, one at a time, every year.....every dam year. :)