after paying buyers changes mind opens dispute

How can a buyer buy item@buy it now price and pay with Paypal then not answer any further contacts I.E..invoice-e-mails -e-bay responses-contact buyer-in regards to pick-up or delivery of large item and 7 days later files an unortharised credit card payment dispute.I thought you had to log into Paypal with your details to pay for a puchase.I also thought once an item was bought as a buy it now price it was a contracted sale.Now a chargeback dispute is opened with paypal and the seller cant do anything till it is resolved- The e-bay fees for selling and listing and the paypal fees leave the seller out of pocket plus the item is packed and loaded for delivery once Paypal clears payment and states the item can be delivered -should,not the seller be re-imbursed for his costs- My belief is the buyer changes his mind and makes up a story to get out of a purchase which is un-fair to the seller. I dont wish to sound like a winger but if you have loaded  the item on the truck ready for delivery and it sits for a week while the buyer wont communicate it very disapointing to say the least-question is who wins from here the seller or the buyer-