Back logs are huge this time of year due to volumes being shipped so most likely sitting in the back of a trailer at some courier or post office depot waiting to be sorted.
This is probably the worst time to ship right now with the Christmas rush on and all.
Yes, there are delays this time of year, but a tracking number will identify, within reason, WHERE the package actually is.
A shipper on eBay has 72-96 hours to actually ship the product. When you purchase a shipping label direct from eBay, it automatically moves it to "Shipped" status, and the status shows up as "shipping label created". When the package is actually delivered to a carrier, status will change to "Origin Scan", "Delivered to Post Office", something like that (depending on the carrier). If you go to the carrier directly, you have to manually input the tracking information, and it skips the "shipping label created" step. EBay will start to prompt the seller if they don't see that "Origin scan" within the required timeframe. After the carrier has it, their timeliness standards apply (USPS Priority Mail is 5-7 business days in the Continental United States at this time of year).
One nice thing about eBay is that the seller doesn't actually get the money for the sale until a couple of days after the package has actually shipped (origin scan). So it's pretty easy to get your money back if the sale turns out to be a scam or a seller error. After that, you would probably have to file a claim with the carrier.