Related על דמאי 3:3

[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).