'as their system doesn't provide a proof of posting we have no way of verifying this.' 

Their system does provide a proof of posting, I have thousands of them in my desk draw, which when I show to an ebay rep they refuse to acknowledge it.  

You also have no evidence that my items were not posted on time.  Once again I will state that I do have the evidence and have attached a photo to prove it.

Whenever I speak with an ebay rep on chat they always so how happy they are that we have been a great and loyal seller on ebay and how good it is that we are top rated etc etc etc, but ask them to accept some evidence that we have done what we said we have and dispatched our items within the stated time limits and suddenly we cannot be trusted or believed!