If prices rise, is it obligatory for us to inform the seller?

Question : I have seen that a person finds, for example, deals, and takes something cheap, even if he is the seller and it is not being sold. Is this a surprise?

Answer : But did he find this item cheap while he is not selling it at that value? Is it because the seller is unaware, or is that the price? Sometimes the seller is among the unaware and does not know about the change in prices, and perhaps the price increases and he does not know, and this happens often. Prices increase, meaning a single surge. And the seller was at the first price. This is fine, because he knows that the goods, for example, are worth ten, but he made it eight because he is in need, yes?
No, no, he knows this. The man knows that it is worth ten, but he says, "I am not waiting for a man to come and take it for ten." It is from advice to say, "It is worth ten," and he says so. If he says, "It is worth ten," and says, "I am waiting for ten," and returns it for eight, this is the Muslim. It is known that this is better. But do we say that if he did not give it to him, he has cheated him?