Why can you buy dry fruit from an Am Ha'aretz?

Question

Explanation of the following Mishnah is according to the Bartenura, Rambam, Kehati, and Tiferes Yisrael.

The Mishnah in Demai (2:3) discusses the requirements of a Chaveir (one careful regarding tumah and taharah). It says that he may not sell to an Am Ha'aretz either dry or wet produce, as he will come to make them impure, and one may not cause Eretz Yisrael produce to become impure.

Fine. So far, so good.

The next requirement is that he does not buy wet produce from them, as they would have become tamei in his reshus. Since tumah only rests on things that have become wet (Vayikra 11:38), the prohibition is only on things which were wet. Dry produce is entirely permissible.

Why are we not concerned that maybe it became wet in his property and subsequently dried? Whether the impurity touched it when it was wet or after it became wet it should still be considered tamei (see Rashi to above passuk). Why should dry produce be any better than wet produce?

Answer 1

The Tosfos Yom Tov actually answers your question!

(Source from Sefaria.org)

ואינו לוקח ממנו לח. כתב הר"ב אבל יבש וכו' ונאמן עם הארץ לומר הפירות הללו לא הוכשרו וכו'. הכי תני בירושלמי. וטעמא דהא דאין עם הארץ נאמן לומר שלא נטמאו לפי שאינן בקיאין בדקדוק טהרות וטומאות ולפיכך אע"פ שהוא ישראל וישנו בתורה ובמצות אינו נאמן לטהרות כמ"ש הרמב"ם בריש פ"י מהלכות משכב ומושב. והלכך לענין לומר שלא הוכשרו נאמן לפי שאין זה צריך לשום בקיאות לדקדק. [*ועיין מ"ש במשנה ג פרק בתרא דמכשירין]:

And he (the Chaver) may not purchase from him (the Am Haaretz) wet (produce): Rav (Ovadia M'Bartenura) writes however (he may buy from him dry) etc. and we believe an Am Haaretz to say that this produce was not rendered susceptible (to Tumah) etc. and so is it taught in the Yerushalmi. The reason a Am Haaretz is not believed to say that they are not Tameh is because they are not experts in the details of Tumah and Taharah. Therefore even though he is a Jew who knows Torah and Mitzvos he is not believed like how the Rambam says in the 10th perek of Hilchos Mishkav and Moshav. Therefore we believe him when he says regarding (the produce) that it was not rendered susceptible because regarding that (Machshirin) he does not need any expertise.

Based on the Tosfos Yom Tov cited, we put our trust in the Am Haaretz to say if it was rendered susceptible before or not, because he would know about such a concept.

Hope this is helpful!