why is it called a flea market?

Answer 1

The first theory, and the one most popular on the Internet, proposes that the term is a direct translation of the French Marché aux Puces, a large, outdoor bazaar in Paris. This original market earned its name from the critter-infested goods it was rumored to sell
The second theory alleges that the term was coined at a time when the slums and alleys of Paris were demolished and replaced by new construction. The dealers in second-hand goods who lived and worked in these old neighborhoods were forced to flee. The merchants' new gathering place was referred to as the "flee market," which later became "flea market."
The final theory associates the term with New York City's 18th century Fly Market. Apparently, the Dutch name for the market was vlie, which means valley but is pronounced "flea."

Answer 2

If you had an aerial view of the market it looks like a bunch of fleas running around all over the place!

Actually, because there are so many small items for sale and the items are thick like fleas.

Answer 3

because everyone looks like flea as the market. you know if you see them from the sky

Answer 4

I know!
If they were selling fleas - who would buy them??

Answer 5

because its other people's old stuff....back in the day when these started, we were alll less sanitary and sometimes there would be fleas in the clothing and blankets.