If someone is selling a product at a ridiculously cheap price, in a case where it is obvious that a mistake was made in labeling the price, can the consumer take advantage of the mistake and buy lots of the product (before the seller discovers his mistake)? Is there a difference if the seller is a Yid or a goy?
I don’t understand why there would be a difference between buying a little or a lot of the item. If the price is more than 16% lower than it should be, buying it would be considered onaas mammon. This applies even if the buyer didn’t cheat the seller but the seller “fooled himself” and made the mistake. However if the seller knows that he price is very low then it is permitted. Regarding a nochri, we are not allowed to steal or fool them in business, however in this instance the nochri wasn’t fooled in any way, but he made the mistake, it would be permitted to take advantage of it. It is not considered onaas mammon as it doesn’t apply to a nochri.
However when applicable there would be an idea of making a kiddush H-shem, similar to returning the lost item of a goy and informing him that you are Jewish and you want to be fair, and that you want double check that this is indeed the price that he intended to charge. However if there will not be any Kiddush H-shem coming out of it, then you shouldn’t do it.
CH:M 227-1,Rema CH:M 348-2, Pischei Choshen Geneiva 10 ftnt.. 1, 2. Be’er Hagolah CH:M 348-8.