These open-air street markets that sell a wide variety of merchandise at bargain prices, most of it secondhand, have two possible origins.
One theory is that the first such market - the marché aux puces - was in Paris. So many shoddy articles were for sale there that they were likely to gather fleas (puces). Another theory says flea markets date back to Dutch colonial days in Manhattan, when there was a Vallie Market at the valley, or foot, of Maiden Lane. It was abbreviated "Vlie Market" and mispronounced "Flea Market." Customers still flocked to it, however.
This word for "cheap and gaudy" is the slurring of "St. Audrey." A fair in her name was held every Oct. 17 on England's Isle of Ely until sometime in the 17th century. Souvenirs at the fair included lace scarves, called "St. Audrey's lace." These neck pieces, at first treasured articles that sold briskly, declined in quality over time until they became known as cheap and tasteless, or "tawdry lace."
SOURCES: 'The Story Behind the Words,' by Morton Freeman; 'The Encyclopedia of Word and Phrase Origins,' by Robert Hendrickson.