I disagree with the "most" statement, most online commerce ads tracking is streamlined, user clicks on ads, goes to ebay, buys item, ads platform connects click

I disagree with the "most" statement, most online commerce ads tracking is streamlined, user clicks on ads, goes to ebay, buys item, ads platform connects click and purchase through some cookies or fingerprinting and you got reliable tracking. Google obviously tracks lots of people through multiple devises, because they are in eccosystem.