The laws of manufacturing tefillin are quite complex. It is impossible for a layperson to make them properly without being trained. They must be written with halachically acceptable ink, on halachically acceptable parchment. Each letter must be formed according to specific and exacting details. If only one point on a single letter is slightly rounded off when it should be pointed, the entire pair of tefillin can become invalidated. The housings must be perfectly square when viewed from the top. Even the stitches that keep the housing closed must be square when viewed from above, and may be made only with halachically acceptable sinews of a kosher animal. The letters must all be written in order. If a letter was written incorrectly, it cannot be fixed out of sequence. Sometimes one bad letter can invalidate an entire pair of tefillin.

As one of the most important mitzvoth in the Torah, it is imperative to observe it appropriately. When a tefillin is not kosher, it must be repaired or replaced to in order to continue using it to perform the mitzvah. Halacha requires that every man check his tefillin every three and half years. Unfortunately, many people do not check their tefillin at all, often wearing invalid tefillin for quite some time. Through the years, exposure to sunlight, weather conditions, general wear and tear, and other factors can cause a pair of tefillin to become non-kosher. Another unfortunate circumstance is that many people purchase tefillin from the wrong sources in order to get it as cheap as possible, and, more often than not, these tefillin may not satisfy the kosher standards set by the Halacha. Depending on quality and extras, a kosher pair of tefillin could cost anywhere from $600 to $1,500.

Since there are so many laws about tefillin, one should buy them only from an honest source who knows the laws and cares for their compliance. A dishonest man might find a problem, but fix it incorrectly, just to save money. We must be very careful whom we entrust our most precious items with, tefillin being no exception.