Flea market probably has a very literal history. The usual explanation is that the name came from markets selling old clothes, bedding, and furniture, items that people believed might carry fleas.
A well known source is the French phrase marché aux puces, which means market of fleas. English speakers likely adopted the same idea. In other words, the phrase probably began as a warning or a joke about used goods, not as a comment on low prices.
This makes the name easier to understand:
- Old coat: secondhand clothing could be suspected of having fleas.
- Used bed linens: bedding was another obvious source of concern.
- Old furniture: upholstered pieces could also seem risky.
Today, of course, flea market simply means a market selling used, vintage, or inexpensive goods. Most people use the term without thinking about insects at all. But the older meaning helps explain why such a strange phrase became the standard name.