The oldest model that is technically arbitrage are the old school Ad Networks. If you can get audiences assembled from lots of small pieces and sell one big chu

The oldest model that is technically arbitrage are the old school Ad Networks. If you can get audiences assembled from lots of small pieces and sell one big chunk, you make more money overall. With RTB, you can do this "assembling" on the fly and sell with some sort of data enrichment. If impression A is sold as more or less anonymous and you know that impression A is actually a potential customer for brand B, you can sell it to band B for more.