How do ebay sellers offer free shipping?

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How do ebay sellers offer free shipping? I mean do they just add the shipping price to the price of the product and say free shipping to attract more people? But some do autions and how does that work? I see things sell for like a dollar and have free shipping? Do they just get a normal car and just put the product say its a usb into it and send it in normal mail so they dont have to pay for UPS? i really dont know how it works. how do they ship things for free?