eBay Buyer has had item for 18 days, now potentially broken it and opened up Return Request

I sold a headset. The buyer has had the item 18 days now, but yesterday opened up a Returns Request which was automatically accepted by eBay as per the below:

In line with the relevant eBay policy, this return has been automatically approved and we've asked the buyer to send the item back. After the buyer dispatches the item, we'll share the tracking information with you. Please inspect the item before issuing a refund. View the return details. You must issue a refund within 2 days of item being delivered.

They've sent the item back today (it's now in transit) and when I look into the details, the buyer gave the following explanation:

Reason for return: Doesn't work or is defective
Comments: The earphones have come off .

The headset was incredibly well packaged in a purpose made box, so wouldn't be able to move at all, in the way it was packed. The only way the headphones would come off is if the item was taken out of the protective packaging and they were handled forcefully.

Going by the above comment, it doesn't say 'Broken on arrival' or anything to that effect and the 18 days that have passed suggests that they've had an accident with them some time after they arrived, broken them and now believes they can return for a refund.

Worst of it is, this was one where a percentage was getting donated to charity too, so they might lose out.

I just wondered where I stand on this when eBay has automatically approved the return. The buyer didn't contact me at all.

I'll see what condition the item comes back in, but any advice would be appreciated.

Thanks