[Freak_NL]

I wonder if those ads are counted as leading to a sale because they are shown right after someone buys one.

Someone goes to the online store of an outdoor shop:

* buys a snowboard (perhaps they were recommended it by someone, or the reviews look good),

* tracking leads to them being shown ads for snowboards in period X,

* tracking also adds the fact that they bought a snowboard in period X (albeit before the ads came),

* ad brokers algorithms, naively or maliciously, conclude that their ads led to the sale,

* companies buying ads conclude that targetted advertising is the most effective way to advertise.