In the print world, it would be like WaPo selling its advertisers on 100K copies circulated to ABC1's, but actually handing a quarter of the papers out for free on Skid Row.
Publishers who buy traffic should absolutely know that the traffic is unqualified, unknown viewers... the least valuable. That means the publisher is selling ads based on their best qualified customers but delivering a fraction of dregs along with them. The publisher plays an arbitrage game with their reputation.
That practice can't help but make the advertisers discount the value of digital ads.