Multiple failed delivery attempts by Parcelforce. Who is responsible? Buyer or seller?

[nbcherry]

Long story, kept short.

Item sold 14/06/17. Despatched (with proof) 15/06/17 by Royal Mail Parcelforce 48. Tracking service reports delivery attempted 19/06/17. Notification card left for recipient. Package returned to depot.

PHASE TWO - Recipient arranges for new delivery on 24/06/17. Nothing arrives. No notification card left. Recipient complains to me. Whilst I am complaining to Parcelforce, recipient messages that it's okay because he has made new delivery arrangements.

PHASE THREE - Recipient arranges for delivery 08/07/17. Again, nothing arrives. No notification card left. Recipient complains to me again, suggesting that he is considering requesting a refund.

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I appreciate that, by eBay rules, the goods have been in transit for over seven working days. On the other hand, none of the delay is of my making. I am not a retailer. The goods were pre-owned (and described as such). Therefore, certain consumer protection legislation does not apply.

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I seek to clarify the position. Am I obliged to refund the buyer then seek redress from Royal Mail Parcelforce? Would it be appropriate to take this matter to the eBay Resolution Centre?

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If the buyer and I accept that the Parcelforce tracking information is accurate up until the 19/06/17 delivery attempt, how is either of us supposed to account for the whereabouts of the package after then? 

In the event that the package has been lost, damaged or stolen whilst in the hands of Parcelforce, who is liable for this? 

I only have the recipient's word for it (and some scanned "documents") as proof that the 24/06/17 delivery failed. I am alert to the possibility of this being a scam. 

At the time of this writing, I have notified Parcelforce that the package remains unaccounted for. A Parcelforce representative is supposed to telephone me about this matter on Monday.

UPDATE: 12/07/17

I reluctantly accept the "solution" provided below as the correct answer. It reinforces my opinion that eBay rules are currently so heavily biased against sellers that the only sensible option is to use other outlets.

[norseway53 · Accepted solution]

There is no case that you can open for this.  Your buyer either receives the goods or you refund in full.  eBay will force the issue when the buyer escalate an item-no-received case to them.