Is it permissible in Sharia to trade a product for which a "maximum subscription price" is set, and in which subscribers submit competitive bids without knowledge of each other's bids, then the highest bidder wins, and a small amount is taken from the losing subscribers?

Auction sales are permissible, whether through public announcement or by each participant submitting their price secretly. Al-Bukhari even dedicated a chapter to it. However, it is not permissible to obligate participants to pay an entry fee or subscription from which the auction organizer or one of the participants benefits, except for the cost of the terms and conditions booklet, provided it does not exceed the actual cost, or a earnest money deposit which must be returned to every participant on whom the auction does not settle. If the entry fees are not returned to the loser, or if the auction organizer benefits from them, or if they are given to one of the participants, then that is forbidden gambling, because it involves financial risk. This website combines selling and gambling, and it collects money from gamblers to complete the price of the commodity, and also takes a share for itself. Therefore, it is obligatory to avoid this.