Spent some time a few years back working in web analytics and my experience was similar to what ChuckMcM describes above - advertisers were relatively sophistic

Spent some time a few years back working in web analytics and my experience was similar to what ChuckMcM describes above - advertisers were relatively sophisticated in general and wanted to pay for performance rather than impression. There are certainly agencies/networks that will waste you're money in advertising if you're not paying attention in digital or traditional media but controlling fraud wasn't terribly difficult. Lots of advertisers would run their own beacons to check and make sure they were getting the audience they were sold. The thing that made them the most nervous was when they couldn't audit their campaigns and the person measuring the audience was the same one selling it.