i posted an item by second class post,but the buyer says he hasn't received yet

Royal Mail don't call items lost inland for 15 days but the seller doesn't have to wait that long.

Now they've opened a case then reply through the case that you will refund them in full if the item does not arrive in a reasonable time.

If the item doesn't show up in the next couple of days then refund the buyer in full and use your proof of posting to make a claim from Royal Mail for your lost parcel.

You need to wait 15 working days before making your claim to Royal Mail and you'll need your proof of posting and a form P58 whcih you can pick up at any Post Office or download from the website.

Items do sadly get lost in the post from time to time - hopefully you've put a return address on it so it may come back to you eventually.

As the seller you are responsible for getting the item safely to the buyer.

To win the dispute you would need to enter a tracking number which proves actual delivery to the buyer.

As you did not use recorded delivery you do not have any such number.

You need to refund the buyer as soon as possible. You do not want them to escalate the dispute. Disputes opened against you harm your account. Those which are escalated do even more damage.

You need to have enough money in your paypal account to make a refund, so upload money from your bank account if you don't have enough in your paypal balance. You cannot fund a refund with a credit card payment.

You will have to claim from Royal Mail for your loss using your proof of postage.