Related על דמאי 3:13

[With respect to one who] sends [produce to another], whether [through] an am ha'aretz or [through] a chaver, he [presumably, the sender] needs to tithe it. Rabban Shimon ben Gamliel says, [if he sends it] to an am ha'aretz, he [the sender] needs to tithe it, and [if he sends it] to a chaver, he [the chaver] needs to know (i.e., that it needs to be tithed, and therefore the sender doesn't need to tithe it). Rabban Shimon ben Gamliel said, it so happened that Rabbi Yosah son of Rabbi sent me a large etrog from Tizippori, and he said, "This came into my hands from Caesarea." And I learned from this three things: first, that it was certainly untithed, [second] that it was impure, and [third] that the [messenger] only had this one [etrog] in the hands, for if he had in his hands another one, he would have taken tithes from that one for it (i.e., on behalf of the etrog that was delivered to Rabban Shimon ben Gamliel).

A chaver that was selling [produce] in abundance and [which] was tithed, and he was assigned something that was Demai, he needs to inform [the purchaser] because everything that is Demai, one needs to inform. Rabban Gamliel used to feed his workers Demai (see Dem. 3:1), and he let them know. But if a homeowner [has already] informed them about the same type [of produce (i.e., that he subsequently sells or provides them)], then he doesn't need to inform them [again].

[With respect to] one who buys vegetables from an outdoor market, behold, this one spends the entire day [deciding what produce to] select, and we need not be concerned; [however] it is forbidden for him to make up his mind [while holding the produce in one's hand but before purchasing it, see Dem. 3:2], [since] he cannot return it, because he needs to tithe, and he cannot tithe it, because [if he changes his mind and returns the produce to the seller] it will be short some quantity [because he has tithed it], and he cannot buy just one item [constituting priestly portion, while returning the rest (per Lieberman)], lest another [buyer] comes and buys [the returned portion], and [unwittingly] tithes already-tithed produce in exchange for untithed produce [see, e.g., Dem. 5:3].

[If someone] left produce at the place of an am ha'aretz, behold, they are presumed [to retain their previous status] for tithing and for Shevi'it (Dem. 3:4, cf. Y. Maas. V.1.8), and if they were subject to tithing, we may take Terumah (the priestly portion) and tithes from it for [produce] in another place (see Bava Metzia 38a:5), or designate Terumah and tithes for them. If they were from second tithe, we exchange them for money, and exchange the money for second tithe. If the [am ha'aretz said], I took [your produce] and left you old [produce or] tithed [produce], if you believe that he took it, we also believe that he purchased [the old or tithed produce], but if you do not believe that he purchased it, you do not believe that he took it. What are we talking about here? At a time that the [chaver] came an found the same type [of produce] that he exchanged, but if he left higher-quality [produce] (see Jastrow = "עגרון") and found lower-quality [produce], or [he left] lower-quality [produce] and found higher-quality [produce], behold, this is a concern, and for this [produce we do not presume it has retained its former status with respect to either] tithes or the seventh year.

One who leaves behind [tithed] produce at the place of a Samaritan, behold, they are presumed to [retain their status] for tithes and for Shevi'it, and if they were untithed, he takes Terumah and tithes for them from another place (i.e., from other untithed produce, see Maasr. 5:6), or he designates the Terumah portion of the tithes from them. If they were from second tithe, he exchanges them for money, and he exchanges the money for the second tithe. If [the Samaritan] says to him, "I took it and I exchanged it for you for old [produce] in its place," or "[I exchanged it] for tithed [produce]," behold he should not be concerned about them (i.e., the produce) with respect to tithes or with respect to Shevi'it.

One who leaves [tithed] produce at the place of a Gentile, behold, he should be concerned [that it was switched for untithed produce] as to tithes and Shevi'it. Rabbi Shimon ben Gamliel and Rabbi Shimon say, "The Jew's produce makes [all] the Gentile's produce Demai." (See Dem. 3:4-5.)

One who [brings his grain to be] milled at the place (i.e., the mill) of an am ha'aretz or the place of a Samaritan, he need not be concerned about impurity (cf. Dem. 3:4). One who [brings his grain to be] milled at the place of a Gentile, behold, he needs to be concerned about impurity.

A person gives [his produce] to an innkeeper to cook a dish for him, and she puts down the pot in front of him, and empties out its contents (see Toh. 2:1 ("מְנַעֶרֶת אֶת הַקְּדֵרָה")), even [if she is a] Gentile, there is no need for concern. (Cf. Dem. 3:5.)