Gemara

56a (Mishnah): Ona'ah does not apply to slaves or land.

56b (Beraisa): The verse forbidding Ona'ah says "v'Chi Simkeru... mi'Yad Amisecha." It refers to something acquired from hand to hand. This excludes land, which cannot be moved, and slaves, which are equated to land.

60b (Mishnah): One may not be Mefarches people, animals or Kelim.

(Beraisa): One may not be Mesharbet animals or inflate intestines, or soak the meat in water.

Question: What does Mesharbet mean?

Answer #1 (Chachamim of Bavel): It is to give to them bran water to drink.

Answer #2 (Ze'iri): It is to comb with a thick comb.

Shmuel permitted putting silk fringes on a cloak. Rav Yehudah permitted to starch clothing with colorful designs. Rabah permitted stretching hemp garments (to show off the fine threads). Rava permitted putting designs on arrows. Rav Papa bar Shmuel permitted putting designs on baskets.

Question (Mishnah): One may not be Mefarches people, animals or Kelim.

Answer: It is forbidden only for old Kelim, for it makes them look new.

Question: How does Pirchus apply to people?

Answer: It is like the case of the slMefarches regarding people is like the case of an old Kena'ani slave who dyed his (white) hair and beard black.

Chulin 113a (Rav Huna): One must salt meat, and then rinse it.

This is when the butcher already rinsed the meat. If he did not, the buyer must rinse it, salt it and rinse it again.

Rishonim

The Rif brings our Gemara.

Nimukei Yosef (DH Ein Mesharbetin): Making the hair stand up makes an animal appear fatter.

Rambam (Hilchos Mechirah 13:15): If one hired a worker, Ona'ah does not apply, for it is as if he acquired him temporarily, and Ona'ah does not apply to slaves.

Rambam (18): I say that Ona'ah applies to a Kablan, e.g. one hired to weave or sew a certain garment for 10 Zuz.

Rambam (18:2): One may not be Mefarches people, animals or old Kelim in order that they will look new. One may be Mefarches new Kelim, to polish, iron and beautify them as much as necessary.

Rambam (3): One may not be Mesharbet people with bran water or similar things to them and fatten the face. One may not dye the face with rouge or similar things. One may not inflate intestines or soak the meat in water or similar things.

Rosh (4:24): One may not be Mefarches old Kelim. It is permitted for new Kelim.

Perush ha'Mishnayos: Pirchus is fixing and beautifying.

Poskim

Shulchan Aruch (CM 227:33): If one hired a worker, Ona'ah does not apply, for it is as if he acquired him temporarily. Ona'ah does not apply to slaves.

Terumas ha'Deshen (318, brought in Bach 45): The Rambam says that Ona'ah does not apply to a (regular) worker, because he can retract in the middle, for Bnei Yisrael are Hash-m's slaves, not people's slaves. A Kablan cannot retract. However, even a worker is equated only to an Eved Ivri, but not to an Eved Kena'ani. We exclude slaves from Ona'ah because they are like land. This is only for an Eved Kena'ani! However, Kidushin 28a equates an Eved Ivri to land regarding oaths. It seems that the same applies to Ona'ah.

Shach (95:18): Megilah 23b proves that a Yisrael is like land. It requires 10 to estimate the value of a Yisrael, just like for land. Sanhedrin 15a, Kidushin 7a and 28a connote similarly. Tosfos says that only Eved Kena'ani is equated to land. The Sugyas oppose this. Surely, we learn all people from slaves. Why should they be different?

SMA (51): A Mishnah (56a) lists things to which Ona'ah does not apply. The Maharshal says that even so, one may not deceive about their value. This is no less than Ona'as Devarim and Geneivas Da'as (deception).

Pischei Teshuvah (21): Sefer ha'Chinuch (337) brings from the Ramban (Vayikra 25:15) that Ona'as Mamon applies to everything. Land (and slaves) is (are) excluded only from returning Ona'ah.

Ya'avetz: It seems that there is no Isur regarding an Eved Ivri, since he is not acquired permanently. He is like a poor Yisrael; it is a Mitzvah to support him. The same applies to to Amah Ivriyah. All the more so one may be Mefarches and beautify a Bas Yisrael so she will be pleasing in the eyes of someone proper for her and he wil be Mekadesh her, even if she is unattractive. R. Yishmael did so (Nedarim 66a). This is if she is merely unattractive. If she has a blemish that is grounds to disqualify Kidushin, Pirchus to cover it up is the ultimate Ona'ah. In the end she will leave (be divorced) amidst disgrace and without a Kesuvah. One can ask about dying an old woman's hair to make her look younger, if she is not so old that she wobbles when walking, which is a Mum. It seems that if she is too old to have children and one covers it up, this is a great Ona'ah and she is divorced.

Divrei Yatziv (EH 15:2): Why did the Gemara discuss only slaves? Ona'ah also applies to women, e.g. Shiduchin!

Rashash (56b DH Davar): Ona'ah does not apply to slaves, but one may not deceive regarding their value, like we find later (60b). One could distinguish; it seems that we do not distinguish.

Shulchan Aruch (228:9): One may not be Mefarches people, animals or old Kelim, to dye the beard of a slave whom one wants to sell, in order that he will appear young.

SMA (16. citing the Tur): One may not dye old Kelim, for he increases the price more than they increase in value. One may dye new Kelim, for in any case they are new and good.

Sho'el u'Meshiv (1:210): The Rambam (Hilchos Avodah Zarah 12:10) forbids dying a white hair black due to Simlas Ishah (adorning oneself like a woman). What is his source? The Gemara asked how Pirchus applies to people, and answered 'like the case of the slave.' The Mishnah connotes that it discusses Stam people, but Rashi explained that it discusses an Eved Kena'ani destined to be sold. According to the Rambam, the Gemara asked what is the case of Pirchus, for a Yisrael may not dye his hair due to Simlas Ishah. We needed to say that the Mishnah discusses slaves.

Note: We could say that Pirchus applies to women, either single women who need not cover their hair, or even a married woman (she may let other women see her hair). Seemingly, the Mishnah forbids Pirchus regarding sales. If so, regarding people we must discuss slaves! However, it could discuss an Eved Ivri, or a prospective worker who wants his employer to think that the worker is young. I do not know a source to say that Simlas Ishah does not apply to slaves.

Shulchan Aruch (ibid): One may not give bran water to animals to drink to inflate the intestines and make the hair stand up. One may not be Mekader (scratch with a Magredes (comb for animals) or thick toothed comb) or Mekartzef (with a Magredes or thin toothed comb) to make the hair stand up, or dye old Kelim in order that they will look new. One may not inflate intestines in order that they will look fatty and wide. One may not soak meat in water to make it appear white and fatty.

SMA (16): Chulin 113a permits rinsing meat, i.e. where this is the custom, for everyone knows this. They will not think that it is white because it is fatty.

Ya'avetz: One may rinse it a small amount, but not very much.