Subterfuge
There are actually four instances in Jewish Law that may be referred to as subterfuge, or finding a loophole in the law. In Hebrew, this is referred to as “Ha’arama.”
The basis for allowing these rules to be “bent” a little bit, was mainly to avoid causing a big loss of money. The Rabbis weighed this carefully, to be certain that they would not be frowned upon by the general public.
The first case of הערמה involved the selling of Chametz to a non-Jew for the duration of Pesach. Originally, it was directed towards sellers of alcohol, who were unable to sell their inventory before Passover.
The Prozbul instituted by Hillel during the Sabbatical year, was permitted when the laws of Shmitta, were rabbinical. With a document and the help of Beit Din, debts could be extended beyond the Sabbatical year.
Similarly, the Heter Mechira, where entire fields were sold to non-Jews during the Shmitta year, was permitted, when these laws were rabbinical. It was meant to save the farmers from monetary loss.
The fourth case allowed for the taking of interest, by creating a kind of partnership agreement. This was called, “Heter Iska.” The banks in Israel usually place this agreement in a place where their clients can see it.
It is important to understand the thought that went into these special laws. They were established by great and compassionate sages.