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

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.