This temple market is supposed to have been established after the captivity, when many came from foreign lands to Jerusalem. Lightfoot says: “There was always a constant market in the temple in that place, which was called ‘the shops’; where, every day, was sold wine, salt, oil, and other requisites to sacrifices; as also oxen and sheep in the spacious Court of the Gentiles” (Horae Hebraicae).
The money-changers made a business of accommodating those who had not the Jewish half-shekel for the annual temple tax. See note on Matthew 17:2424And when they were come to Capernaum, they that received tribute money came to Peter, and said, Doth not your master pay tribute? (Matthew 17:24) (#674). Every one, rich and poor, was expected to pay the half-shekel for himself during the month of Adar. It thus became necessary sometimes to change a shekel into two halves, or to exchange foreign money for the Jewish half-shekel. The men who followed this business made their living by charging a percentage for the exchange, and carried on their traffic within the temple area.
Loftus found a curious resemblance to this practice in the court of the mosque of Meshed All at Nedjef: “A constant fair is carried on at stalls, which are supplied with every article likely as offerings to attract the eye of the rich or pious among these, white doves are particularly conspicuous” (Travels in Chaldea and Susiana, p. 53).