Rules for guarding money given to a normal person, merchant, or money-changer: Bava Metzia 43a
If sanctified money was given to a money-changer to guard, and he used it, who is guilty of trespass: Bava Metzia 43a
Miscellania
Moneychangers tend to be expert in the value of coins; laypeople cannot readily evaluate coins as they would evaluate merchandise: Bava Metzia 52b
On the 15th of Adar, special money-changers were established to aid acquisition of the Half-Shekel for its donation to the Temple: Megillah 29b
On the 25th of Adar, special money-changers were established in the Temple itself to aid acquisition of the Half-Shekel for its donation to the Temple: Megillah 29b
How often did money-changers set up shop in urban and rural areas: Bava Metzia 52b