While the early evolution of digital media buying and selling was based primarily on the need for advertisers to find new channels, the quick growth of the industry and the number of sites that advertisers had to choose from soon made the idea of direct buying and selling pretty much infeasible. As a result, ad networks sprung up to give digital advertisers more of a "one-stop shopping" option that allowed them to advertise on many sites with only a single media buy. But they brought with them some questions about the quality of the audience targeting and the value of the impressions that were being purchased.
