Was it the £500 + digital bundle item?
Personally, I would not agree now to it being collected as you would have no proof that the item was 'delivered' / collected.
Message the buyer if they wish to collect you will cancel the order, which will refund them if they have paid, and relist it as a Collection only item. This after purchase and payment eBay will email them a 6 digit collection code. They must bring this code with them, item will not be released without it.
This code is essential to scan or manually enter the numbers on collection, as it's the only proof of collection.
If you cancel selecting the reason Buyer Requests to Cancel, this will not affect yur seller performance.
One important tip, if you wish to proceed this way make it very, very clear in your eBay messages that you are cancelling for the item to be relisted immediately on eBay , as a Collection item for the buyer to buy from the eBay listing. You can even repeat it's being relisted .
eBay read all messages going through their system leave the message clear that item is not being removed for an off eBay sale.
@rossross1976