Chapter 3, Mishna 2, 3
A valid eruv may only be established with food that is ritually fit for use, to the exclusion of untithed produce and unredeemed consecrated produce. What about demai, doubtfully tithed produce? Or improperly redeemed produce? We need not place the food for the eruv in its designated location ourselves, but we must send a qualified agent, to the exclusion of minors, imbeciles, Sadducees, Samaritans and others. Who were the Samaritans and why did they try to undermine the Jewish people? May we send an unqualified agent as courier if we have a qualified agent at the location to receive the food for the eruv? Should we be concerned that the unqualified agent will not actually deliver the food, or the qualified agent will not actually accept it from the unqualified agent? No, because we have a legal presumption that an agent fulfills his agency (or else why would the principal appoint him?).