I use the Chrome browser almost exclusively on Incognito mode. When shopping online, I religiously close all Chrome sessions, fire them back up on incognito mode and start browsing for purchases.

Curiously enough, the items start showing up as suggestions when I log into Facebook. Initially, I dismissed them as artifacts of a unlogged-out facebook session, so I started paying more attention. Then I thought maybe the vendor (eg: amazon.com, hotels.com, walmart.com etc.) was sharing it because the suggestions were advts for shopping with that vendor, which made little sense to begin with since I have separate logins. Then I noticed targeted suggestions for sites I do _not have an account with (eg: tripadvisor.com) but where I was browsing at anyway.

I use the same computer to access facebook and online shopping but I'm never logged into the former when doing the latter. I dutifully close my incognito sessions after every shopping instance. Further, I am incognito on Chrome for both.