But in print it is knowable how many copies are going out, isn't it?

Even that can be fiddled.

USAToday used to do it via deals with hotels to put one outside your room. Boom, extra copies!

Yeah although ad buyers of any sophistication knew going in that a lot of certain newspapers were hotel copies (though arguably a lot of people read those), trade rags vs. consumer subscriptions, general vs. niche, etc. and took that into account.

They still didn't have a great idea of how effective they were a lot of the time of course.

Printing a newspaper at least costs a bit more money and there's a decent chance someone will read the copy of the paper in their hotel room. Fake Web traffic could easily dwarf real traffic.

Advertisers would want to know something akin to circulation numbers before paying for placement though. And they would want to be reasonably confident those numbers aren't pumped by fraud.

Maybe the web needs something like Nielsen ratings, where Verified real users voluntarily submit their browsing to help advertisers determine watch time.

I talk about this at the end of the post as well. I think a ratings panel approach doesn't apply well to the web because the web is so fragmented. (In a good way! I like that there are lots of independent sites!)

Unless you had something like 10% of real users or a super representative 1% I think you'd have a big problem with getting realistic numbers outside huge sites.

Yes. But even if you pay for a month placement on a given site, the ad buyer is still going to want an estimate of how many legitimate viewers see/saw your ad.

It probably works better on things like podcasts but the bottom line is that you can't really trust me to tell you how many viewers my site had without some fraud detection mechanisms in place. (And even then fraud is apparently pretty rampant.)

I may be missing something, but why? Wouldn't the buyer just look at how many people arrived at their website from the ad?

How do you know those clicks are people? (You can measure just conversions but that's a much higher bar for measuring an ad and a direct conversion may not even be your objective.)

Bots can click through like any other visitors. They won't buy stuff, though, so if you're placing ads for people to directly take an expensive action ("performance advertising") you're mostly ok. Brand advertising, though, is very dependent on fraud detection because it doesn't have this clear connection.

There's more about this near the end of the post.

Do you think it’s possible to measure how many people are coming from an ad on a specific site and buying something, without also resorting to illegal tracking?

That's a good point. I think a shopping site might be able to succeed in arguing that they had a legitimate interest in tracking how people arrived on their site, but possibly not. On the other hand, if half of your visitors consent to tracking that's enough to have a pretty good sense of the value you're getting from each source.

>But even if you pay for a month placement on a given site, the ad buyer is still going to want an estimate of how many legitimate viewers see/saw your ad.

yes, you might WANT that. but you do not NEED that. Remember that ad's isn't only effective when clicking on it, but also by spreading visibility of your offer/product.

you could easily use sites visitor count as a estimate for monthly pricing. And frankly without all tracking there would be no incentives to fake click on ads at all, so you could get your own tracking on your own side.

If I can't tell with some degree of assurance whether you have 1K viewers per month or 1M viewers per month (never mind uniques), I'm probably not going to pay for ad on your site.