Ketubot 86 - Trust
An oath is a serious thing, and nobody can impose an oath on a person at will, not even a court. There must be a reason, such as the case where one admits to part of the claim and says, "It is true that I owe you money but less than what you say." Then the oath is in order.
However, if the husband appointed his wife a storekeeper or an overseers for his business, he can ask for an oath any time, without a definite claim. Actually, this applies to any business partner, of whom one may have suspicion of embezzlement.
Rabbi Eliezer says that the husband can impose an oath in any case, because it is unavoidable that the wife is an overseer over her spindle and dough. But the Sages say, "One cannot live with a snake in the same basket." That is, if the husband suspects her so much, the wife may not be able to live with him.
Young Italian Woman from Papigno with Her Spindle by Jean-Baptiste-Camille Corot