[Quoth]

Search on Amazon UK market place for ebooks and Amazon USA for ebooks is now so bad that putting amazon site, title and author into Duck Duck Go works far far better.

They have now also disabled purchases of ebooks for a Kindle on Amazon US if they decide it's not on a US Residential Address.

Irish Kindle users can elect to purchase on US site in Dollars, instead of UK site in Sterling, but it seems an illusion. Books vanish from USA site when you log in. The price seems mostly the same, but not always. The vanishing books, if on ebooks.com, will become unavailable if you try to buy there.(1, 2)

But UK order by Price may be using US prices as it's often wrong?

Search by author or Series on UK seems to return the USA results so you can't find books with a UK title differing from USA unless you look up the UK title elsewhere.

It's broken.

1)
So other evils for digital sales are IP Geolocation. People travel and it can be defeated by a a VPN.

2)
The crazy world of demarcated territories and digital rights by territory. Other goods too. It's a kind of cartel and outdated by 70 years. For English it was the agreed carve up of the world between USA and UK companies. Even done with batteries.
Makers like UK Burberry won a court action to prevent an Irish company importing from USA. All duties & VAT paid. Real goods, not counterfeit. Levi Strauss (USA) have also won such cases.
Yet the goods in many cases are made in a 3rd country. It's an imperialist & Colonial attitude to world retail and consumers.

It's time that any one anywhere should be able to buy any ebook, even almost anonymously if legitimately paid for. It seems worst for English. But I suspect issues with Spanish, French and Portuguese ebooks.