I know you have a Shipping comment in your listing description that mentions couriers (see screengrab below), but I think you need to make it more clear that you will be using a courier.  The words "Standard Delivery - registered" does not scream courier to me.

I am not available at home for courier delivery and I have a PO Box.

I would like to think that I would read your full description and see the Shipping part, but the postage and handling makes no mention of freight, which is the word I associate with use of couriers.

Lesson for me is to make sure I do read all of the description of items I am interested in and not just rely on the P&H tab.