The following link seems fairly reliable in explaining how the Amazon's bestsellers rank works:
http://www.makeuseof.com/tag/8-things-people-dont-know-amazons-bestsellers-rank-sales-rank/In a nutshell the rank is based on volume of sales relative to all other sales in that particular category.
Carol Ann Lee's current position = 654
http://www.amazon.co.uk/The-Murders-White-House-Farm/dp/0283072210Paul Harrison's current position = 92,205
http://www.amazon.co.uk/Deviant-Jeremy-Bamber-White-Murders/dp/190409192XYou need to move down a fair way on the above links to get to the best-selling rank.
As a guide Amazon have produced the following based on best seller rank and typical sales per day based on the rank:Amazon Best Seller Rank 50,000 to 100,000 – selling close to 1 book a day.
Amazon Best Seller Rank 10,000 to 50,000 – selling 5 to 15 books a day.
Amazon Best Seller Rank 5,500 to 10,000 – selling 15 to 25 books a day.
Amazon Best Seller Rank 3,000 to 5,500 – selling25 to 70 books a day.
Amazon Best Seller Rank 1,500 to 3,000 – selling70 to 100 books a day.
Amazon Best Seller Rank 750 to 1,500 – selling 100 to 120 books a day.
Amazon Best Seller Rank 500 to 750 – selling120 to 175 books a day.
Amazon Best Seller Rank 350 to 500 – selling175 to 250 books a day.
Amazon Best Seller Rank 200 to 350 – selling 250 to 500 books a day.
Amazon Best Seller Rank 35 to 200 -selling500 to 2,000 books a day.
Amazon Best Seller Rank 20 to 35 – selling 2,000 to 3,000 books a day.
Amazon Best Seller Rank of 5 to 20 – selling3,000 to 4,000 books a day.
Amazon Best Seller Rank of 1 to 5 – selling4,000+ books a day.
So according to the above Carol Ann Lee is selling between 120 - 175 books a day; Paul Harrison is selling 1 book per day.Well done Carol Ann Lee

I wonder which author will be top of the charts next week &%+((£