Is it considered Najsh (deceptive bidding) for the auctioneer to bid on an item to raise its price without authorization from the owner, and without the intention of buying it?

Al-Najsh is unlawful. It is to bid up the price of a commodity without genuinely intending to buy it, but rather to deceive others. If one bids up the price to benefit the seller, even if not intending to deceive others, it still falls under the forms of Al-Najsh.