Is it permissible to buy and sell on a website that stipulates accepting the last displayed price for an item after the auction period ends, even if it is significantly lower than its original value, knowing that entering the website implies agreement to this condition?

The sale is invalid if the price is unknown, such as selling a commodity for whatever price the market settles on. This is due to the prohibition of gharar (uncertainty) in sales, and because it is unknown whether the price will settle at a high or low amount. This could lead to consuming the seller's wealth unjustly if he is compelled to sell for less than the commodity's value.