When I first got my Kindle I would diligently check amazon.com vs Amazon.co.uk for the cheapest deals and switch back and forth between them as you could quite often save 3-5 currency units by purchasing from one site or the other.
Those sort of large differences seemed to die off when the agency pricing model came into effect, but I still sporadically check, just to make sure. Today I found a situation where Amazon appears to be messing with me.
The left most window shows amazon.co.uk when I'm not logged in, the middle window shows amazon.com when I'm not logged in, the right most window shows amazon.com when I am logged in. If I'm logged in on amazon.co.uk, it refuses to give me a price at all and points me to amazon.com. The URL of the two amazon.com pages is different (I got to each by searching for "winter of the world in kindle store" and clicking the first link), but attempting to go to the "cheap" amazon URL in my logged in browser, just says "pricing information not available" and refuses to let me buy it.
amazon.co.uk URL: http://www.amazon.co.uk/Winter-World-Century-Trilogy-ebook/dp/B0071BGOJC/ref=sr_1_1?s=digital-text&ie=UTF8&qid=1348005072&sr=1-1
cheap amazon.com URL: http://www.amazon.com/Winter-World-Century-Trilogy-ebook/dp/B0071BGOJC/ref=sr_1_1?s=digital-text&ie=UTF8&qid=1348005120&sr=1-1&keywords=winter+of+the+world
expensive amazon.com URL: http://www.amazon.com/Winter-World-Century-Trilogy-ebook/dp/B007FEFLTO/ref=sr_1_1?s=digital-text&ie=UTF8&qid=1348005006&sr=1-1&keywords=winter+of+the+world
The two cheap books share an ASIN, while the expensive book appears to be an entirely different item alltogether, but is the only copy of the book that Amazon will let me buy with my account.
Very weird.