User Activity

I have a listing which I wish to cancel. If I go to 'modify my listing' and scroll to the bottom there is a 'cancel' button. But this does not actually cancel my item. I have tried several times, it just repeatedly asks me to sign in, which I do. But...
I have just sold an item to someone who joined eBay today and has zero feedback. They have paid through Paypal. I am a little suspicious - can the buyer 'pull any tricks'? Should I send the item by registered/recorded post? Can the 'buyer' retract th...