The only guaranteed antidote to this kind of fraud is performance advertising (pay per sale). I think pay per click and pay per impression, though arguably useful for brand advertising, will always be vulnerable to sophisticated scams like this.
It's guaranteed, but it probably won't work: "Thanks for doing business with us -- by the way, where did you hear about us?" "Online, but I forget where."
Advertisers need to be able to associate an advertisement with a result. Otherwise the effectiveness of advertising is a myth.
So as good as CPA sounds, its not full proof either. You can just bypass it with either stolen credit card purchases or refunds.
> That PPS is a more trustworthy metric than PPC.
Yes, true, but only for sales that follow directly from an advertisement, with no intervening time or context changes.
I agree with the basic argument the PPS is more reliable and meaningful, but it would be worthwhile to know how many sales follow directly from an initial advertising exposure, as opposed to a more complex decision-making process.
Consider the diamond campaign waged by De Beers described in another HN thread today. The advertising costs were high, but the goal was to change consumer perceptions over a period of decades (and successfully). This is far removed from the model we're discussing, essentially an impulse purchase -- the De Beers campaign wasn't directly correlated with diamond sales at all.
My point is that not all advertising can be shoehorned into a directly trackable purchase, yet those other kinds of advertising might still be valuable.
And believe me, i'm not arguing in favor of tracking -- only presenting the most often heard argument.