Why am I held responsible for the USPS failings?

[carartman]

I have a problem with how ebay calculates late shipping & validated tracking information. I offer next day shipping, and have never failed to send out an item on the same or next day. 100%, Yet my validation has fallen below 90%. How can they hold me resposible for the failure of the USPS to scan tracking promptly. If I lose my top rated standing because of something I can't control, I'll leave ebay.  Even if the USPS loses a package, I am considered at fault.