Are they within 30 days of the item's last estimated date for delivery? If they are and they open a case of item not as described, you will have to accept the case and refund, as cases are all automated, no human contact.
Afterwards you can appeal the decision, if you think the refund was unfairly granted, the link below explains the process.
https://www.ebay.co.uk/help/selling/managing-returns-refunds/appeal-outcome-case-seller?id=4369
I won't admit it's easy, eBay do not see the item and do tend to side with the buyer. However, you never know the buyer may have a history of doing this, or making too many returns and refunds, eBay have full access to their account, and if this is flagged up, it will go in your favour.
@hripana0