Related su Demai 3:4

[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.