Mishnah 8 in Chapter 4 of Tractate Bechoros also deals with the law of a suspected person - this time, a person suspected regarding the Seventh Year, meaning violating the prohibitions associated with the Shemitah year. To understand the words of the Mishnah, we must first introduce the fundamentals of the halachah on this subject.
Prohibitions of the Seventh Year and the law of sefichim:
By Torah law, it is forbidden to work the land during the Shemitah year, and it is also forbidden to deal with Seventh Year produce in a regular commercial manner.
On the other hand, plants that grow on their own during the Seventh Year are permitted by Torah law. For example, after the wheat harvest, a few kernels drop and are scattered by the wind, and the following year stalks of grain grow from them on their own - nature takes its course. These plants are called "sefichim", and on a Torah level they are permitted to eat.
The Sages came and prohibited sefichim, meaning any species that only grows if replanted year after year: vegetables, grain, and legumes - they are all prohibited by rabbinic law during the Seventh Year. The reason for the decree: people disrespected the laws of Shemitah and grew crops illegally, and then claimed about the wheat they grew: "This wheat grew on its own, they are sefichim" - while in truth that was not the case.
And who is the suspected person? A person known to have a history of trading or selling produce that he grew illegally during the Seventh Year, and he violates Shemitah. In such a case, one may not buy produce from him during the Seventh Year, since he cannot be relied upon.
"Chashud lashviis ein lokeiach mimenu pishtan" - one who is suspected regarding the Seventh Year, one may not buy flax from him:
The Mishnah teaches a novel concept that we do not buy even flax from him. Flaxseeds are edible and even healthy to eat, but a person does not grow the plant for the seeds alone; from the wording of the Mishnah it emerges that flax is grown primarily for the stalks, which are used to produce linen fabrics and textiles. Nevertheless, one may not buy flax from him, meaning the raw material for producing textiles, out of concern that he planted it during the Seventh Year and is lying.
"Va'afilu seirak" - the law applies even if he already combed the flax fibers. In the previous Mishnah we saw that when a person has invested a great deal of toil and is afraid of losing all his time and effort, there is room to be lenient, since he has much to lose. However, combing the fibers does not involve a great deal of trouble and does not require significant time and effort, and therefore he is liable to do so even though he risks having the merchandise confiscated - for the flax material came into his hands for free, forbidden material to be sure, but without payment.
"Abal lokchin mimenu tavui ve'arig" - but we may buy from him spun and woven items:
Flax products that underwent further processing - it is permitted to buy them from him. "Tavui" means that it was spun into threads, as we saw in the previous Mishnah. Since spinning flax fibers into threads involves a great deal of toil, a person does not risk doing this just because he obtained cheap and forbidden raw material; he will ensure he has kosher and proper material, lest his merchandise be confiscated and he ends up suffering a loss.
"Arig" means a woven item, and here the question we asked in the previous Mishnah arises once again: If it is already permitted to buy threads from him due to the multitude of labor, all the more so that it is permitted to buy woven fabrics and garments from him, since weaving a sheet and the like requires much more toil than spinning a thread.
The Gemara explains that "arig" here is not stated in its usual sense - fabric woven into a sheet, a blanket, or a garment - but rather braiding alone, for the purpose of making a rope: flax ropes made of flax that was not spun into threads at all.
Thus the Mishnah is teaching: Whether the flax was spun into threads, or whether it was not spun but was twisted and braided into ropes - it is permitted to buy from him, and we are not concerned lest this is flax that was planted, grown, and traded in a commercial and illegal manner during the Shemitah year.
In summary: In this Mishnah, we learned the law of one who is suspected of violating Sheviis. We prefaced this with the foundational principles of the halachah: the Torah prohibitions against working the land and doing business with Sheviis produce, the Torah allowance for sefichim (aftergrowths), and the rabbinic decree forbidding them because of those who disregard Shemittah. From here we discussed the law regarding flax: we may not purchase the raw material from him, even if he combed it, since this involves minimal effort and he has nothing to lose; but we may purchase spun and woven goods from him - threads and braided ropes - since he would not risk having his merchandise confiscated after investing such extensive labor.