Gemara

(Rava): Even if Shamai holds that Yesh Shali'ach l'Devar Aveirah, he admits that if Levi sent Shimon to have forbidden Bi'ah or to eat Isur, Levi is exempt and Shimon is liable. We never find that the one who benefits is exempt, and someone else is liable.

Bava Metzi'a 10b (Ravina): Ein Shali'ach l'Devar Aveirah only when the Shali'ach is Bar Chiyuva (liable for transgressing).

(Rav Sama): Ein Shali'ach l'Devar Aveirah only when the Shali'ach can choose whether or not to comply.

They argue about a Kohen who told a Yisrael 'be Mekadesh a divorcee to me', or a man who told a woman 'cut a boy's sideburns for me.' Rav Sama exempts the Meshale'ach, and Ravina obligates him.

Me'ilah 20a (Mishnah): If Reuven told Shimon "give one piece of meat to each guest," and Shimon told the guests to take two each, and the guests took three each (and the meat was found to be Hekdesh), everyone was Mo'el.

21a (Mishnah): If Reuven told a Cheresh, lunatic or child to bring money (which was Hekdesh) to a grocer, if he fulfilled the command, Reuven was Mo'el.

Question: Such a person (without understanding) cannot be a Shali'ach!

Answer #1 (R. Elazar): It is as if he is a bucket (that holds olives):

(Mishnah) Olives are Mekabel Tum'ah once they emit moisture in the bucket.

Answer #2 (R. Yochanan): This is like the case of Eruv (Techumim):

If one put (food for) an Eruv on a monkey or elephant and it took it to the desired place, the Eruv is valid.

Summation of both answers: The bucket or animal has no understanding, yet) it performs Shelichus. The same applies to a Cheresh, lunatic or child.

Rishonim

Rif and Rosh (Kidushin 16b and 2:2): Actions of David's Shali'ach are attributed to David, unless he was told to do an Aveirah. Then, we say that he should have listened to Hash-m, not to David.

Question (Tosfos Kidushin 43a DH she'Lo): Regarding Me'ilah, the Shali'ach benefits and is exempt, and the Meshale'ach is liable. This refutes Rava!

Answer (Tosfos): The Meshale'ach is liable (and the Hekdesh becomes Chulin) once the Shali'ach picks it up, before he benefits. If a Shali'ach told to put his hand into oil and benefit from anointing with it, without lifting it, the Ri was unsure whether the sender is liable, or if the Shali'ach is liable, due to Rava's law.

Rambam (Hilchos Me'ilah 7:1): If Reuven told Shimon "give one piece of meat to each guest," and Shimon told the guests 'I allow you to take two each', and the guests took three each (and the meat was found to be Hekdesh), all were Mo'el.

Rambam (2): This refers to meat of Bedek ha'Bayis. If the meat was of an Olah, only the ones who ate were Mo'ei, for there was another Isur in addition to Me'ilah. The only Shali'ach l'Devar Aveirah is Me'ilah with no other Isur involved.

Question (R. Chaim ha'Levi, on Hilchos Me'ilah 8:1): The Rambam discusses Me'ilah for eating, for there is no Isur to lift an Olah. Why must he say that Ein Shali'ach? In any case, Reuven is not liable for what Shimon eats!

Answer (R. Chaim ha'Levi): One is liable for Me'ilah for stealing from Hekdesh, even without Hana'ah. Indeed, Ein Shali'ach regarding the Hana'ah, but Reuven can be liable for the theft, if no other Isur is involved.

Maharit (Kidushin 42b (on Rif) DH ul'Devar): Yesh Shali'ach also regarding slaughtering and selling, and Shlichus Yad! If a Shomer told someone to be Shole'ach Yad, the Rambam obligates the Shomer due to negligence, not due to Shelichus. The Gemara called this Shenei Kesuvim, for if we could learn from Me'ilah, we would not need a verse regarding Shlichus Yad. (If he incited thieves to take it, this is like an action). Also regarding slaughtering and selling, the Torah punishes for benefit, even without Shelichus.

Hafla'ah (Kesuvos 33b DH v'Chi): The Tur (CM 350) says that even if the thief commanded the Shali'ach to slaughter on Shabbos, Yesh Shali'ach. He holds that this is unlike Me'ilah, in which Shelichus is needed. Here, he is liable for benefit. R. Yochanan and Reish Lakish (Bava Kama 68b) obligate a thief for a sale even before despair, even though it does not take effect. Here also, even though the Shelichus is Batel due to Ein Shali'ach, the thief is liable. The same applies to commanding a Shali'ach to slaughter to idolatry.

Rebuttal (Sha'ar ha'Melech Sof Me'ilah): Also Me'ilah does not require Shelichus (Me'ilah 21a)! The Gemara asked why Yesh Shali'ach for Me'ilah, i.e. we should say that an adult acts for himself, not for the Meshale'ach.

Defense (Kehilas Yakov (Kesuvos 38): We can distinguish between Me'ilah through benefit and through Hotza'ah (removing from Reshus Hekdesh). One who sends Hekdesh to a grocer is Mo'el because the sender is Makneh (transfers ownership) to the grocer. The Shali'ach merely delivers it. The questioner thought that the sender must do an act. We answered that it suffices that his will was done. The Rambam discusses Me'ilah through benefit. Then, Shelichus is required. Any other Isur is Mevatel the Shelichus. Tosfos (Me'ilah 21b DH Nosno) says that Yesh Shali'ach for Me'ilah of Hotza'ah, but for Me'ilah through Hana'ah, like Rava taught.

R. Meir Simchah (Kidushin 42b DH v'Al Pi): The Shali'ach is commanded not to eat Olah. He must arouse himself to be aware of the Isur (except for Me'ilah, in which Yesh Shali'ach), not the Meshale'ach. Since the Shali'ach was not careful, the entire Shelichus is Batel. Or, perhaps the Rambam (Perush ha'Mishnayos Me'ilah 6:2) exempts the Meshale'ach when he was Shogeg and the Shali'ach was Mezid, unlike Tosfos (Kidushin 42b DH Amai). Since the Shali'ach was not careful about the other Isur, it is as if he was Mezid and acted for himself, not for the Meshale'ach.

Question (Pnei Yehoshua): According to those who are stringent to say that Yesh Shelichus l'Nochri, why is telling a Nochri to do Melachah on Shabbos only mid'Rabanan? Since the Nochri is not Bar Chiyuva, Yesh Shali'ach l'Devar Aveirah, so the Meshale'ach transgresses mid'Oraisa!

Answer (Beis Meir EH Sof Siman 5): Shabbos is like a Mitzvah on a person's body, that he rest on Shabbos. Shelichus does not apply, just like one cannot make a Shali'ach to wear Tzitzis (Tosfos Rid Kidushin 42b DH Sheani). Therefore, a command to slaughter on Shabbos does not Mevatel Shelichus.

Divrei Yechezkeil (57:2): One may not start to burn (Pasul) Kodshim before Shabbos if it will burn on Shabbos. The Yerushalmi (Shabbos 2:3) explains that the Torah considers this an (important) Melachah, even though the person rests on Shabbos. Shechitah does not require Shelichus. The thief is liable even through a child.