Sgt_Kickaxe - 9:00 pm on Jan 9, 2013 (gmt 0)
My granny has no addons besides the default and she rarely uses her computer. She bought a book from amazon and a book from a Google affiliate network partner using two different sites of mine and I did not get credit for the sales. I think this is more common than many affiliates believe it is, some insiders have even warned people off about affiliate programs when they leave the company.
I've also seen an affiliate report in which several dozen sales were registered over a period of three days in which the click time being reported was the same. This amounted to several thousand dollars in revenue that undoubtedly belonged to several affiliates. The affiliate company was part of a major network and responded by saying everything was fine, keep the money. It wasn't fine and the 100 fold increase in results only lasted those three days.
They make mistakes, tracking is not an easy game and it only keeps getting harder.