Sutten1

I know im a bit late to the game here, I may be wrong, but as far as I am aware it is based off amount of sales per times viewed. So if you have a item (item A) that is not popular, has narrow range of keywords , and only shows up in search if someone enters a very specific keyword , it may lets say have only 20 views. If you do sell 1 copy of this item its sale ratio should now be 1 sale per 20 views Your popular item (Item B) has more chance being shown in search, clicked on but not purchased, for example you may have sold 200+ copies but your views may be 9,000+ your ratio for Item B is lower so it shows up after Item A so while Item A has only sold 1 copy, the statistics of someone buying based on only on views is greater