So far, we have discussed two types of ona'ah, pain that you could cause somebody: ona'ah in business transactions, where you mischarge somebody very differently from the market value, and ona'at dvarim, where you are paining somebody with your words.
Here, we'll talk about a third type of ona'ah, an unethical business practice. The Mishnah says that if a person is selling produce or grain and announces that he is selling grain from a certain field, he is not allowed to take grain from a different field and mix it into the grain he is marketing as coming from that field. If you're saying that it's grain from a certain field, you have to actually sell grain from that field. You can't add grain from another field. If you're selling new grain from one field, you can't take new grain from another field, even though there's no difference in quality. Your word is your word, and you have to stick to it. You can't rationalize or justify mixing different grains, even if they're the same quality. Obviously, you're not allowed to mix new grain into old grain if you promised people that you were going to sell them old grain. Old grain has advantages: it's more dried out and therefore produces more flour. So, obviously, you can't do that.
Really, halachically (according to Jewish law), the hachamim (the Sages) say that when it comes to wine, the hachamim did allow a person to mix a certain amount of stronger, sharper wine into a softer, more mellow wine, because the sharp wine improves the quality when it's added to the softer wine. So, even if somebody marketed soft, mellow, not-so-sharp wine, he would be allowed to mix in a certain amount of stronger, heavier wine, because that automatically enhances the flavor and potency of the wine. When you're making it better, of course, you can give a person the better end of the deal.
Whenever a person is selling wine, there's an expectation that there will be some sort of sediment, which is particles of grape that settle at the bottom of the barrel. The person buying it understands that he may receive some sediment. Here, the Mishnah is going to tell us that if I sell a small amount of wine from the top of a barrel and there's no sediment in it, I don't have to sell wine with sediment in it. Taking wine sediment from a different barrel and putting it into the clear wine of this barrel would ruin the wine. You may rationalize and say, “You know what? There's no sediment coming out of this barrel, and therefore I'm losing out a little in terms of filling up the bottle. I usually fill it up with 97% wine, and 3% sediment comes out, so I save that 3%. Here, it's coming out as clear wine, 100% wine. Let me take some sediment from a different barrel and mix it in. The customer isn't going to know the difference. He isn't going to know how full the barrel was originally, and he's getting the same amount of wine that he usually gets.” He's not allowed to do that; it would ruin the wine. You're allowed to give the buyer regular sediment from your own barrel, from that actual wine. You're allowed to sell that to him. A little bit of sediment is expected.
You're not allowed to dilute wine. If it's being marketed as undiluted wine, that would just be theft. So, here we'll talk about what happens if a person already has wine that was diluted with water. You're not allowed to sell it in a store in small amounts to people unless you tell them straight out that there's water mixed into the wine. You cannot fool them. You're not allowed to sell it to a wine salesman even if you inform him that there's water mixed into it, because we're concerned that the person receiving this wine will take it and fool people. He'll cheat his customers and tell them it's pure wine without water in it, so we're not allowed to help him in that endeavor. But in a place where it's very customary to add water to wine and then sell it, and therefore the customer should already expect that, the seller is allowed to add water because the buyer understands and expects that there will already be water in his wine.