I do not know, nor I expect would you, what exact process eBay uses to implement the bidding agency they provide. Maybe it is scripting, maybe it is a program, maybe it is a whole cohort of pacific rim minimum wage earners at consoles typing away. It doesn't make a difference. The actual bidding is out of my hands and in the hands of my agent -- Ebay.
No, it isn't eBay. They give you scripting that you implement when you set your bidding. You script it when you add your fields and execute it by confirming bid. You are launching a macro.
You are still in control with the option of withdrawing a bid.
A bid on an auction board is an electronic signature. You are signing a contract. You are acting on your behalf.