In "Biblical Perspective" Randall McElwain writes:
The moneychangers and them that sold doves operated in the Court of the Gentiles, a large court that was open to Gentile visitors. Because the annual half-shekel Temple tax had to be paid in a standard Temple coin, moneychangers were able to charge exorbitant rates for changing the Roman currency into Temple money. In addition, the priests controlled the sale of doves and sacrificial animals, which were greatly overpriced. These transactions were necessary; foreign money had to be changed to Temple coin, and it was more convenient to purchase animals for sacrifice at the Temple than bringing them long distances. However, Jesus objected to the unjust exchange rates and inflated prices, as well as to the spirit which turned a “house of prayer” into a bazaar.
Discussion: What exactly was the injustice Jesus found at the Temple? Was it that animals were being sold and that money was being exchanged? Or was it something else?
Source: Jesus, Son of God: Adult Teacher's Insights, page 72.