"There is no intention to sell the cover." - Nonsense, why hold stock like this if not to sell it.
Mark Bloxham is one of the top-end dealers in the UK, often taking 20-page adverts in the philatelic media. If you think this is just because of free listing days (which probably don't apply to
ebay store-owners anyway), click on 'see other items' and select 'highest price first'. You will then see more £100,000 items including stamps ex the Royal Collection, 1d black paper and gum trials, multiple 2d blues on cover, etc.
This is a show-case worldwide, and reaches a far bigger audience than the printed magazines. Some of the same items are listed on the company website (
https://philatelic.co.uk/product-ca...nny-blacks/) but
ebay is just another marketing avenue. I wouldn't expect these to be sold on
ebay, but rather sold by negotiation as a direct sale.