The Halacha of Ona'a is that if an item was sold for more than 1/6 difference in real value the buyer and or seller can cancel the sale.

How is Ona'a figured on for example fresh salmon? There are stores that sell it for as high as $12.99 lb and stores that sell it for as low as $6.99 lb. Is Ona'a 1/6 less than $6.99 and 1/6 more than $12.99?

  • 1
    "real value" actually I believe it's market value.
    – yydl
    Commented Oct 20, 2010 at 4:22
  • but market value is defined by what people will pay for it, so it is a bit of a catch-22
    – Jeremy
    Commented Dec 17, 2010 at 18:23
  • 1
    Rabbi Breitowitz acknowledged that taking ona'a naively, you would say that if all the producers conspired to raise the price of a specific item, they're then selling it at "the going price" so it's not ona'a. (Presumably, the prohibition was intended at the scale of the individual merchant.) Though we do have a source that food should not be sold at a price beyond twice its cost to the retailer.
    – Shalom
    Commented Dec 17, 2010 at 18:50
  • Related: judaism.stackexchange.com/questions/31184/… they must be merged I think
    – Al Berko
    Commented Jan 30, 2019 at 16:21
  • Very related: "how-to-beware-of-the-prohibition-of-onaa" judaism.stackexchange.com/questions/99049/…
    – Al Berko
    Commented Jan 31, 2019 at 13:49

3 Answers 3


Are you getting the same thing from both stores? Seems to me that the wide price disparity is due to difference in quality, either of service or product, or some other factor. Absent any material difference, there's no question that the higher-priced store is ripping you off.

  • A very important distinction that almost no Poskim make!
    – Al Berko
    Commented Jan 29, 2019 at 13:37
  • A very important distinction that many poskim make... Minchat Asher 3, Mishpetei Aretz on Ona'ah, Pitchei Choshen 11:1 and 13, Otzar HaMishpat vol. 2, Moznei Tzedek 3 CM 25 all attempt to figure out how to calculate ona'ah nowadays given modern day developments like this.
    – MDjava
    Commented Jan 4 at 2:33

Heard from Rabbi Herschel Welcher:

The problem with ona'a is only when fooling the buyer by making them think that your vastly-inflated price is the normal going price for this item. (Or vice versa.) But if you take what is reasonably known to be a 99-cent product and are selling it in some incredibly convenient location for $2, that's not ona'a.

So a given store's price could have to do with quality, location, convenience, all sorts of other factors. What you can't do is tell a customer "yes it seems expensive, but any grocery store around here sells the exact same product for this price" if that's not true.

(Specifically with regards to salmon, whether you get wild-caught or farmed, Atlantic or Pacific, whether it's product of China, etc. -- can make a huge difference. Not every pound of salmon is the same!)

  • 2
    This is a good explanation of the exorbitant prices at the kosher stand at Camden Yards. location, location, location!
    – Jeremy
    Commented Dec 17, 2010 at 18:25
  • This is totally wrong (your second paragraph)! 1. Ona'a works both ways 2. Ona'a is even when the buyer knows the average price 3. Ona'a holds when they both don't know the prices at all.
    – Al Berko
    Commented Jan 29, 2019 at 13:40

Here's a simple table to explain how Ona'ah works (from Mesivta on B"M 51a): enter image description here

Please note, Ona'a works both ways for the seller and the buyer. It also can be calculated (a Machlokes) either out of the product's value (if a product costs $6, the both $5 and $7 would be within 1/6th of the product's cost - $1) or out of the money paid ($6 paid will work for both $5 and $7 products).

Although we all see the contradiction, this is how Shu"A rules in C"M 227

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