From BiblePortal Wikipedia

Hastings' Dictionary of the Bible [1]

Money-Changers . How indispensable were the services of the ‘money-changers’ (  Matthew 21:12 ,   Mark 11:15 ), ‘changers of money’ (  John 2:14 ), ‘changers’ (  John 2:15 ), and ‘exchangers’ (  Matthew 25:27 AV [Note: Authorized Version.] , RV [Note: Revised Version.] ‘ bankers ’) in the first century of our era in Palestine may be seen from the summary of the varied currencies of the period in the preceding article (§§ 6. 7 ). The Jewish money-changer, like his modern counterpart the sarrâf (for whom see PEFSt [Note: Quarterly Statement of the same.] , 1904, p. 49 ff., where the complexity of exchange in the Palestine of to-day is graphically set forth), changed the large denominations into the smaller, giving denarii, for example, for tetradrachms, and gave silver for gold, copper for silver. An important department of his business was the exchange of foreign money and even money of the country of a non-PhÅ“nician standard for shekels and half-shekels on this standard, the latter alone being accepted in payment of the Temple dues (cf. money, §§ 4. 6. 7 ). It was mainly for the convenience of the Jews of the Dispersion that the changers were allowed to set up their tables in the outer court of the Temple (  Matthew 21:12 ff.). The wealthier members of the profession, the ‘ exchangers ’ (RV [Note: Revised Version.] ‘ bankers ’) of   Matthew 25:27 (cf.   Luke 19:23 ), received money on deposit for purposes of investment, on which interest was paid (see Usury).

The money-changers had constantly to be on their guard against false money. This gives point to the frequently quoted unwritten saying ( agraphon ) of our Lord to His disciples: ‘Be ye expert money-changers’ be skilful in distinguishing true doctrine from false.

A. R. S. Kennedy.

Watson's Biblical & Theological Dictionary [2]

in the Gospels, were persons who exchanged native for foreign coin, to enable those who came to Jerusalem from distant countries to purchase the necessary sacrifices. In our Lord's time they had established themselves in the court of the temple; a profanation which had probably grown up with the influence of Roman manners, which allowed the argentarii [money-dealers] to establish their usurious mensas, tables, by the statues of the gods, even at the feet of Janus, in the most holy places, in porticibus Basilicarum, or in the temples, pone aedem Castoris. The following extract from Buckingham's Travels among the Arabs, is illustrative:—"The mosque at the time of our passing through it was full of people, though these were not worshippers, nor was it at either of the usual hours of public prayers. Some of the parties were assembled to smoke, others to play at chess, and some apparently to drive bargains of trade, but certainly none to pray. It was, indeed, a living picture of what we might believe the temple at Jerusalem to have been, when those who sold oxen, and sheep, and doves, and the changers of money sitting there, were driven out by Jesus, with a scourge of cords, and their tables overturned. It was, in short, a place of public resort and thoroughfare, a house of merchandise, as the temple of the Jews had become in the days of the Messiah."

Smith's Bible Dictionary [3]

Money-changers.  Matthew 21:12;  Mark 11:15;  John 2:15. According to  Exodus 30:13-15, every Israelite, who had reached or passed the age of twenty, must pay into the sacred treasury, whenever the nation was numbered, a half-shekel as an offering to Jehovah .

The money-changers whom Christ , for their impiety, avarice and fraudulent dealing, expelled from the Temple were the dealers who supplied half-shekels, for such a premium as they might be able to exact, to the Jews, from all parts of the world, who assembled at Jerusalem, during the great festivals, and were required to pay their tribute, or ransom money in the Hebrew coin.

People's Dictionary of the Bible [4]

Money-changers.  Matthew 21:12;  Mark 11:15;  John 2:15. According to  Exodus 30:13-15, every Israelite who had reached the age of twenty must pay into the treasury, whenever the nation was numbered, a half-shekel as an offering to Jehovah. The moneychangers whom Christ, for their impiety, avarice, and fraudulent dealing, expelled from the temple were the dealers who supplied half-shekels, for such a premium as they might be able to exact, to the Jews from all parts of the world who assembled at Jerusalem during the great festivals, and were required to pay their tribute or ransom money in the Hebrew coin.

Morrish Bible Dictionary [5]

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.  Matthew 21:12;  Mark 11:15 .

Hastings' Dictionary of the New Testament [6]

MONEY-CHANGERS. —See preced. art. and Bank, No. 1.

International Standard Bible Encyclopedia [7]

chān´jẽrs ( κολλυβιστής , kollubistḗs , from κόλλυβος , kóllubos , "a small coin," so "a money-changer," or "banker" (  Matthew 21:12;  Mark 11:15; "changers" in  John 2:15; compare  John 2:14 , where κερματιστής , kermatistḗs , "a dealer in small bits," or "change," is also rendered "changers"); compare τραπεζτης , trapezı́tēs , "one who sits at a table," "a money-changer," "a banker" or "broker"; one who both exchanges money for a small fee and pays interest on deposits ( Matthew 25:27 , the King James Version "exchangers," the American Standard Revised Version "bankers")): The profession of money-changer in Palestine was made necessary by the law requiring every male Israelite who had reached the age of 20 years to pay into the treasury of the sanctuary a half-shekel at every numbering of the people, an offering to Yahweh, not even the poor being exempt. It seems to have become an annual tax, and was to be paid in the regular Jewish half-shekel ( Exodus 30:11-15 ). Since the Jews, coming up to the feasts, would need to exchange the various coins in common circulation for this Jewish piece, there were money-changers who exacted a premium for the exchange. This fee was a kollubos (about 31 cents in U.S. money, i.e. in 1915), hence, the name kollubistēs . The Jews of Christ's day came from many parts of the world, and the business of exchanging foreign coins for various purposes became a lucrative one, the exchangers exacting whatever fee they might. Because of their greed and impiety, Jesus drove them from the courts of the temple.