A buyer on eBay arranged own courier and he didn’t receive the item, he opened a paypal claim and has gotten a full refund (see details)?

Is someone asking you for money for something?  Your question isn't clear. Is this something YOU sold? or something you BOUGHT?  Restate this more clearly. 

It is the seller's responsibility to ensure that the item the customer bought is delivered to the customer.   There is no getting around this.

You were not required to allow the customer to use that courier. 

At the very minimum YOU should have hired the courier so that if THEY don't do what YOU hired them to do, YOU have recourse.   But you didn't do that.

You handed someone's item off to a stranger that you had no business agreement with and therefore they have zero responsibility to you.

ETA:  "If his agent took the goods, you are entitled to be paid for them."  Normally this is true.   However, the seller agrees to certain responsibilities and policies when they agree to use the eBay and Paypal platforms.  

I’m the sellor I’ve tried but they say for data protection they can help as only the person who arranged it can see to it. 

The seller should contact the courier and inquire about it since they were the agent for the buyer and it was last tracked as being in their possession.

Hold the courier responsible and file theft charges against them if need be. You have proof that they had the item, but they can't prove it was delivered.

Yes.  PayPal was his method of payment.  The courier was acting for him, not you.  If his agent took the goods, you are entitled to be paid for them. 

As a seller, NEVER use paypal.  

The sellers always lose on ebay, you can challenge it in court but I don't know if you'd win, you might have to sue the courier and not him but then they can turn around and say it's not insured. Don't let them arrange their own courier next time.