Is it permissible, in Islamic law, to sell online by concealing the price and only displaying it privately, while manipulating it by raising or lowering it based on buyer interest?

For a sale to be valid, the price and the item sold must be known with a clarity that prevents dispute. There is no harm in the seller concealing the price until contacted; this is not considered cheating or deception. The variation in price based on the strength of demand is natural and achieves justice. Deception enters when the buyer is led to believe a certain price or non-existent discounts, or through exaggeration in describing the product. The Prophet, peace and blessings be upon him, said: "Whoever cheats is not of me," and "Deceit, deception, and treachery are in the Fire." The fundamental principle for prices is the absence of fixed determination, leaving them to the influence of supply and demand, and leniency should be exercised in buying and selling. It is not permissible to exploit the buyer's need by raising the price beyond the market value. The seller may waive part of the price for some people, such as friends and relatives. However, the seller is not permitted to deceive people by raising the price for the ignorant and selling at the usual price to the shrewd; rather, the price must be uniform for everyone.