Anybody get many 15% commission sales at Amazon.co.uk?

We only have direct links to books at Amazon UK. Therefore, sales should earn us 15% commission.

However, because of Amazon's tricks (e.g. must add book to shopping cart before going to any other page at Amazon) the last ten book sales we've earned have all earned only 5% commission.

I can understand how some of them might be reduced down to 5% becuase of the various get-outs that Amazon employs, but all of them? Surely not.

So I wanted to ask: do any webmasters earn much 15% commission? Big difference between 5% and 15%.

The only time I seem to get 15% is when I order a book my self and make sure I add it to the basket before going anywhere else!