I recently bought a small electric pressure washer from WalMart on-line and had several on my watch list. Now I just received an email telling me I won a free pressure washer from Harbor Freight. I reported it as spam of course but the point is anything you view, anything you buy is being tracked and watched. That's why the gov't wants to end currency where people will have to use a CC and leave a paper trail so they can snoop.
It seems to me though that trackers would want to keep separate files. Someone viewing an item is showing interest in that item and could possibly fall for such a scam of "if you want it here's one for free".
Someone who has bought an item is not going to be interested in getting another one so they're targeting the wrong crowd there.