I see nothing wrong with the Buy Now option disappearing after the first bid. If you want the item right away, use the button before anyone puts a normal bid in. Having the Buy Now option is a luxury, anyway, as you'll see it's not a requirement when listing on eBay. It's a convenience for both the buyer and the seller, as it can save time for both parties. If it's not going to save time, then the seller should have the potential to make more than the Buy Now price.