I don't know about this. The idea that it should be centrally reviewed and managed is somewhat of a strawman as far as I'm concerned. Once you outlaw third-party advertising you would naturally expect such directories to spring up (much like specialized business publications that are actually full of high-value ads that genuinely serve a purpose for people in the business) but they could operate just like normal businesses with in the capitalist system and would have to compete for quality and customers.