This is a common problem when items are to be collected.
It's easier if the buyer simply doesn't pay, because you can open an unpaid item case after four days.
When they've paid you can't risk cancelling the sale. If you refund the buyer without their agreement to cancel eBay treats you as having refused to sell, and places a very damaging defect on your account.
As has been said, it's best to give the buyer more time - it's only been a week, and some buyers take much longer than this to get round to collecting. They can afford to wait, because eBay gives them 30 days and Paypal gives them 180 days in which to claim their money back if they don't receive it - even if it's because they never collected it!
You will find that the rules on eBay are very much in the buyer's favour.
