Gambling is betting on an uncertain outcome. The uncertainty is not in whether you can the item (you can get it if you keep bidding forever). What's uncertain is whether you will get the item for less than its value. This is what makes it a gamble.

You define the outcome as winning the auction. That's dishonest. The outcome is whether you'll spend more or less than buying the item outright at retail price, which is what you are competing against.