These days I try to look past the technical notion of it being a 'case opened against me', because, like you say, a lot of the time the buyer is just trying to communicate with the seller, and eBay have decided to formalise this communication as well as provide limited options for actions by the seller.
It's not necessarily always easy, if I'm honest, because for years the entire concept of disputes and cases were something bad to do to a seller, especially without prior communication, but now they're going hand in hand so I'm trying to look past that, and more look more at just the accompanying message that the buyer has sent if / when determining whether the buyer is being reasonable.
