Commentary for Shevuot 7:5

שניהם נשבעים ונוטלין מבעל הבית (i.e., the storekeeper and the workers) – the storekeeper said to hi, the workers are not believable to me with an oath; you declare them as trustworthy for you did not say to me with witnesses, “give to them.” And similarly, the workers say to him: “The storekeeper is not believable to us with an oath.” But when both (i.e., the storekeeper and the workers) take an oath frand take from the owner of the house, they take an oath, one in the presence of the other, that just as that the storekeeper is frightened from the workers or the workers [are frightened] from the storekeeper.

“And the shopkeeper with his account book,” How so? Not that he [the shopkeeper] says to him [the customer], “It is written in my account book that you owe me two hundred zuz”. Rather he [the customer] says to him [the shopkeeper], “Give my son two seahs of wheat,” or, “Give my laborer small change to the value of a sela” and then he says, “I have given,” and they say, “We have not received”; he [the shopkeeper] takes an oath, and receives [his due from the customer]. And they take an oath, and receive [their due].
Ben Nanas said: “How can both be permitted to come to a vain oath? Rather he takes without an oath, and they take without an oath.”
The mishnah which we will learn today discusses the fifth type of person who swears and collects: the shopkeeper with his account book.
This mishnah explains the fifth category of person who swears and thereby collects: the shopkeeper with his account book. The mishnah first explains that this is not a case where a shopkeeper claims that it is written in his book that so-and-so owes him money. In such a case the shopkeeper would not be able to swear and thereby collect from his customer. In that case the customer would be able to deny the debt without even having to take an oath.
Rather the mishnah describes a case where a customer requested that a shopkeeper give his son 2 seah of wheat or his worker coins the value of two sela. The customer promises to pay the shopkeeper back later on. We can see from here that in the time of the Mishnah shopkeepers, who usually had cash and produce on hand, functioned somewhat like a bank. Later on, the shopkeeper claims that he has paid the son or the workers. The son or the workers respond that they have not been paid. In other words, both sides are claiming that the customer/employer owes them money. According to the first opinion in our mishnah the shopkeeper can swear and collect from the customer. He is allowed to do so because he did not have any direct dealings with the son or the workers, direct dealings which would have implied that he trusts them to take an oath that they had not collected. There is no true business relationship between the son or workers and the shopkeeper. Rather there is a relationship only between the customer and the shopkeeper, and the customer and his son or workers.
The workers also may swear and thereby collect their wages from their employer. Since they have no business relationship with the shopkeeper, they need not trust him to swear that he did pay them. They may then swear and collect from their employer as all wage earners do (see mishnah one).
Ben Nanas points out a problem in this situation: if the shopkeeper swears that he did give the wheat or money and the son or employees swear that they didn’t receive, one of them is definitely swearing falsely. By the court mandating that both sides swear, the court is actually encouraging God’s name to be disgraced by a false oath. Rather, Ben Nanas rules that both sides collect without taking an oath.

אלו ואלו באין לידי שבועת שוא – for perforce, one of them takes a false oath and it is found that the name of Heaven is profaned. But rather, both of these (i.e., the storekeeper and the workers) take their money without an oath. But the Halakha is not according to Ben Nanos.