The Mishna on today’s daf lists people who will not be accepted as witnesses in a Jewish court, because they are involved in monetary shenanigans that are forbidden by the Sages. These people include dice players, money lenders who take interest, people who gamble on pigeon races, and those who market produce from the Sabbatical year. Rabbi Yehuda says: ba-meh devarim amurim – “under what circumstances is this rule taught?” When this is their livelihood. If a person has another occupation and participates in these activities only occasionally, then he still could be trusted as a witness in court.
Unlike modern courtrooms where witnesses are asked to swear prior to their testimony in order to ensure that they will tell the truth, a Jewish courtroom believes that every witness who is called to testify will tell the truth. Nevertheless, there are several types of people, enumerated in the Mishnayot of Massekhet Sanhedrin, who cannot testify. Close relatives, for example, cannot testify, no matter how upstanding and honest we know them to be. There are also people whose behavior does not allow the court to accept them. Among them are untrustworthy people who have committed sins that put them in the Biblical category of a rasha.
According to most rishonim, the people mentioned in this Mishna are only disqualified on a rabbinic level. The Mishna is teaching that aside from those individuals who have transgressed biblical law which disqualifies them from testifying in court, there are other people whose participation in activities that show them to be susceptible to the influence of monetary gain makes us fear that they could be bribed or similarly influenced to change their testimony. According to this approach, the “interest” levied by a lender must be forbidden only by rabbinic decree. Others understand the Mishna to also include people who are disqualified on a Torah level. They explain that the Mishna does not mention, for example, thieves and robbers since it is only teaching about cases where the issue is not so obvious, for in all of the Mishna’s cases the victim of the crime hands the money over to his oppressor willingly.