How to handle a suspected buyer scam

[the_walter_mitty]

Hi everyone,

I have been an ebayer since 2004 and I have never had a problem until recently. I have sold an item to a person and they are claiming that their item has not arrived after a couple of days. 1 Week after dispatch, they are now demanding a full refund. I have sent this item as Royal Mail 2nd Class signed for and I have asked the buyer wait until 18 calender days however they seem to be pushing for a refund after one week. Has anyone else experienced this and what can I do?

On the Royal Mail tracking website, it states that they have the item. What happens if I give the buyer a refund only for him to go to the post office the next day to sign for  the parcel? What can I do then?