Eruvin 32: Trusting the System

Following from the discussion of shlichut, sending an emissary - when can you trust that the system will function the way you've set it up to run? When you appoint a shaliach, can you act thereafter as if the shaliach has done his (or her) job? Or so you need to check in before you take the next step? For example, a woman who has given birth and offers a korban before she can dunk in the mikveh to purify. Namely, her dunking presumes that the kohen did his assignment. Plus the case of the "chaver" (one who is learned, knowledgeable) vs. the "am ha-aretz" (one who is ignorant). With the example of Demai - food that isn't clear whether it has had terumot/maaserot taken from it. Making the case for who is more reliable in both directions, perhaps with a little focus to the chaver. Also, a new mishnah! What if you put your meal establishing your eruv techumin up in a tree? Or deep in the ground? The same distance up is not acceptable, while the same distance down counts as a legitimate establishment of your residence, to count as a residence.