In summary, I am surprised to hear a buyer can request a return and this is automatically generated including postage labels without photos being shared first with the seller etc.
That's exactly how ebay works.
Offering a listing with no returns means the seller doesn't have to accept it back if the buyer changes their mind, or has bought the wrong size etc. However, as with any item sold online in the UK, the buyer has the right to return if the goods are faulty or significantly different to the description.
This is a pandoras box when it comes to ebay, as buyers just choose this option regardless of the real reason for the return, and there is no mechanism within ebay for a seller to fight it.
@Bungle when (sadly not if) ebay find in favour of the buyer and refund them, your only course of action will be to jump in the car and confront this person. When purchasing they should have given their phone number. Sometimes a call stating you'll be driving over to see them is enough to get them to drop the case, but i do know of people who have followed through on this promise.