The Prophet, sallallaahu alayhe wasallam, prohibited najash. Najash is trickery whereby one offers a high price for a commodity not intent upon buying it but upon cheating someone else who wants to buy it, even though it is not worth such an elevated price. Scholars have unanimously agreed on the prohibition of such action if the increase in price puts the commodity at a higher price than similar items. This prohibition is based on the hadeeth narrated by Ibn Umar that Allah's Messenger prohibited najsh. (Agreed upon)
Even if the price is increased to the price of a similar commodity, al-jumhoor (the majority of scholars) have gone with the impermissibility of such actions based on the generality of the hadeeth text. Ibn Hazm, Ibn Abdul-Barr and Ibn al-Arabi, however, held the opinion permitting such action. Ibn al-Arabi stated that, "If a man sees a commodity that is sold below its actual value and he increases the value to the correct value, then he should not be accused of najash, especially if he did not have bad intentions." This is supported by the hadeeth narrated by Imaaam Ahmad that the Prophet, sallallaahu alayhe wasallam, said, "Leave the people alone, for Allah sustains some from others. Should one ask his brother for a sincere advice, his brother should give him advice."