Chap 4. Mishna 3/4 deal with overcharging in business of 1/6 profit.
(a) Does this only apply to Jews?
(b) What products does this apply to or all businesses?
(c) Is the 1/6 profit the net profit that one makes or the selling price(gross revenue)?
(d) What is our custom/halacha today?
Richard Herring, South Africa
(a) Does this only apply to Jews?
The source for the prohibition of Ona'ah (cheating) is the verse: Vayikra 25:14. The word "Amisecha" in this verse means, "fellow Jew" (see Rashi there). Therefore, technically this prohibition only applies to Jews. Practically though, it is forbidden to cheat a non-Jew because there is a second prohibition of Geneivas Da'as (fraud) which applies to non-Jews as well (Rema CM 348:2, Shulchan ha'Rav 348:2, Aruch ha'Shulchan 348:2). (There are Halachic authorities - the Meiri in Bava Kama - that say that non-Jews that adhere to a moral code similar to ours must be treated the same as Jews in monetary matters, so even the prohibition of Ona'ah would apply to them.)
(b) What products does this apply to or all businesses?
The prohibition applies to buying and selling all movable objects. It also applies to renting movable objects - such as a car - because when you rent something, you are essentially buying it for a certain amount of time (Shulchan Aruch CM 227:35).
There is a Machlokes whether it applies to land. The Rambam and the Beis Yosef (Shulchan Aruch CM 227:29) say that it does not. Rabeinu Tam and the Rema (227:29) say that it does but the definition of cheating is not 1/6 but rather 1/2. This same Machlokes applies to slaves, therefore the Beis Yosef (Shulchan Aruch CM 227:33) says that it does not apply to hired workers - such as a taxi driver - because a hired worker is similar to a slave. It should follow that according to the Rema, there is Ona'ah by hired workers if the Ona'ah is more than half. It seems, though, that the Rema agrees with the Beis Yosef on this issue (see CM 227:33).
For other services where the worker is not paid an hourly wage but rather is contracted to do the work - such as a plumber or electrician - there is Ona'ah (Sema, there, note 59).
It should be remebered that in all cases where we say that Ona'ah does not apply, we mean if it there was Ona'ah, that the sale stands and the buyer or seller cannot demand their money back. It does not mean - Chas ve'Shalom - that one may willfully cheat his fellow man (Sema, there, note 51).
(d) What is our custom/halacha today?
The laws of Ona'ah are numerous and complex but they are essentially the same today as they are formulated in the Shulchan Aruch. For an actual question in this area, please seek out a competent Halachic authority.
Kol Tuv,
Yonason Sigler