unfair feedback

A customer pays for an item then I post it the next day from country Vic to QLD and about 10 days later I get Neg feedback and a refund request case against me for a undeliverd item due to Australia post now slower system. Totally unfair to get neg feedback in such a short time without the chance to mediate a solution. I think this is where ebay should step in and remove the unfair feedback and this is a new ebayer and could be scaming a freebe unfortiunatly no extra was paid for tracking and the item was a coin that fitted in a letter.