There's not really any meaningful empirical proof of ad impressions now, just a very shady chain of trust between a handfull of companies who all have a vested

There's not really any meaningful empirical proof of ad impressions now, just a very shady chain of trust between a handfull of companies who all have a vested interest in not scrutinizing these things too closely. Once you're at the point where you are buying traffic to meet goals, you're not going to scrutinize the origin of that traffic beyone anything that would appear to be flagrant fraud to your customers.