Etymologyfrom costard + monger
A costermonger was a street seller of fruit and vegetables. The term, which derived from the words costard (a type of apple) and monger, i.e. "seller", came to be particularly associated with the "barrow boys" of London who would sell their produce from a wheelbarrow or wheeled market stall.
Costermongers have existed in London since at least the 16th century, when they were mentioned by Shakespeare and Marlowe. They probably were most numerous during the Victorian era, when there were said to be over 30,000 in 1860. They gained a fairly unsavoury reputation for their "low habits, general improvidence, love of gambling, total lack of education, disregard for lawful marriage ceremonies, and their use of a peculiar slang language" (John Camden Hotten, The Slang Dictionary, 1859). Costermongers were notoriously competitive: respected "elder statespeople" in the costermonger community were elected as pearly kings and queens to keep the peace between rival costermongers.
However, crimes such as theft were actually rare among costermongers themselves, especially in an open market where they tended to look out for one another. Even common thieves preferred to prey on shop owners rather than costermongers, who were inclined to dispense "street justice".
The activities and lifestyles of 19th century costermongers are comprehensively documented in London Labour and the London Poor, a four volume collection of very erudite and well-researched articles by Henry Mayhew.
By the end of the 19th century, the traditional costermonger was in decline, and were nostalgically portrayed in the music halls by vocal comedians such as Albert Chevalier (1861-1923) and Gus Elen (1862-1940).
The antihero star of Look Back in Anger (1956) by playwright John Osborne is a costermonger who sells candies from his cart. The play and a filmed version of it also depict aspects of the formal and informal politics associated with street markets, i.e., racial prejudice, irate customers, abusive regulatory officials etc.