Back in the spring, I had a UPS delivery mark delivered without it actually showing up. This was not an Ebay purchase, but rather from a known retailer who I use a lot(KEH Cameras, if anyone is interested), and I had it delivered to work since they typically ship boxes "direct signature required."
I waited a day or two, then contacted the vendor. They initiated an inquiry with UPS, and it showed up a few days later. I actually saved the shipping box for a while as it had about 6 labels stuck on it that told the whole story-essentially it gave the address of the GPS coordinates of the initial delivery scan, and of the closest address to that those coordinates. Apparently the driver went there, retrieved the package(which hadn't been opened) and then delivered it to me.
BTW, remember that Ebay itself doesn't sell anything-it's a platform for sellers. As someone who regularly uses Ebay, I ship most things by USPS because Ebay makes it easy and pretty much everything I sell is small and light enough that USPS is the most economical choice. With that said, Ebay leaves it up to the seller to use whatever carrier they want as long as it has online viewable tracking/delivery confirmation. I have had things come to be by UPS, Fed-Ex, and even freight carriers-it just depends on what makes the most sense for the item.