Related sobre Demai 6:12

[If] an am ha'aretz who said to a chaver, "Buy me a bunch of vegetables," [or] "[Buy me] a loaf of bread," Rabbi Yosei says, there is no need [for the chaver] to tithe [what he purchased for the am ha'aretz, see Dem. 6:12]. Rabbi Yehudah says, he needs to tithe. Rabbi Shimon ben Gamaliel says, if he exchanges the money (i.e., he uses his own money rather than the am ha'aretz's money to purchase the vegetables or the bread, see Minchat Yitzchak here), he needs to tithe.

[If] five said to one, "Go and bring us ten loaves of bread" [or] "[Go and bring us] ten bunches of vegetables," [and] he brings each one to his face (i.e., he brings that person what was purchased with that person's money), [then the] chaverim that are among them (i.e., among the purchasers) do not need to tithe except for their own portions. [But if] he brings them mixed together [so that he cannot tell which produce was purchased with which money], [then] the chaverim that are among them need to tithe on everything. If they gave him one in addition (i.e., the seller delivered one more item than was ordered, e.g., a baker's dozen), Rabbi Yehudah says, "It belongs to the messenger," and Rabbi Yosei says, "It is in the middle," (i.e., they all divide it, see Y. Dem. VI.8.6 ["רִבִּי יוֹסֵי אוֹמֵר שֶׁל שְׁנֵיהֶן"]).