Make it an automatic thing that after a certain amount of time if they have not ticked "Item Received" or "Item Not Received"  then they will get emails asking them to do so. Not hard to set up and it would then allow the seller to follow up on any dispute before Ebay needed to be contacted thus less work for ebay and more communication and hopefully better resolutions between Buyer and Seller.

by Law if the buyer has an item they paid for it is no longer the property of the seller...what would the dispute be ?