פירוש על בבא מציעא 4:6

בכרכים – where there is a money-changer; until he can show it to the money-changer.

Until when may he [that is defrauded] return the coin? In large towns until he has had time to show it to a money-changer. In villages until the Sabbath eve.
If he [that had given the coin] recognized it, even after twelve months he should accept it [in return], but [if he does not accept it the one who received it] only has a cause for complaint [against him].
And it is permitted to use it for redeeming the Second Tithe without concern, for [he who would not receive it] is but only a cheapskate.
If a person should receive a fraudulent coin (one that weighs less than it is supposed to), he may demand that the person who gave him the coin replace it with a better coin. However, there is a time limit for making such a demand. In large towns where money-changers who could check the coin would be found, he only has as much time as it would take to bring it to a money-changer. In small towns he has until the eve of the Sabbath, since it can be assumed that most people from small towns will visit the market and see money-changers before the Sabbath.
If the person who gave him the coin recognized the coin he should exchange it even after the time mentioned above has long lapsed. However, if he refuses to exchange the coin the person who received it has no legal claim against him. The most he has is the right to make a formal complaint, which may damage the reputation of the person who gave the coin but will not legally compel him to exchange the coin.
Finally the mishnah teaches that one may redeem his Second Tithe with this coin, since anyone who would not accept the coin is only being cheap. The Second Tithe was the second ten percent of a person’s produce. It had to be brought to Jerusalem and eaten there. Since it was difficult to carry all of the produce itself to Jerusalem a person was allowed to redeem the produce with money, and then bring the money to Jerusalem to use it to buy food.

בכפרים – where there is no money-changer.

עד ערבי שבתות – who comes to spend it on Fridays for Sabbath meals, for then he would know if he is able to spend it and receive it (i.e., its equivalent value) from him.

ואם היה מכירה – this is how it should be understood: if he is a righteous individual, and wants to act with equity, if he recognizes that it is the Selah that he gave him, he will accept it from him even after twelve months.

ואין לו עליו אלא תרעומת – this is how it should be understood: and the other who is not a righteous individual and did not want to accept it from him, he has nothing against him other than a complaint/quarrel against him; and he himself who caused him personal loss, in that he did not return it at the appropriate time.

ונותנה למעשר שני – he is speaking of the loss according to the measure of fraud, and he gives it for Second Tithe at its equivalent value, and does not worry because of the uncoined metal which Second Tithe cannot be redeemed for other than a coin which has a form, for it has the name of a coin upon it, and whomever does not take it at its equivalent value as a valid coin, other that something like a piece of silver or gold bar (as opposed to a coined metal), is not other than an evil person.