I'm learning how to scale a profitable campaign, which is an art in and of itself apparently. It's not easy. So I sign up to several traffic sources that claim to have xxx,xxx inventory per day on SPECIFIC carriers. WOW. And then I bid a higher than average bid and get 10k pops per day. My suspicion is that these kinds of traffic sources buy up traffic from other sources and pool them together. High volume, sure, but super expensive. Traffic brokerage - is that a thing? These are convenient for brand advertisers so they don't have to sign up to 10 different sources to buy their media. But for performance advertisers it's hard to get this into green.