Boyd’s Bible Dictionary:
Those who made a business of supplying the annual half-shekel offering at a premium
(Ex. 30:13-15; Matt. 21:12; Mark 11:15).
Concise Bible Dictionary:
These were persons who supplied those who came from a distance to Jerusalem, to pay the regular tax to the temple, with a half-shekel, in exchange for any money they might possess. The Lord’s language to such, when He drove them out of the temple, seems to imply that they took unfair advantage in the exchanges (Matt. 21:12; Mark 11:15).