I think for things like jobs, housing, etc that have protected civil rights the only real way to ensure people's rights aren't being infringed is to make them completely open and post both the ad and the stats of where the ad was served/the settings for the targeted audience depending on the type of . Maybe even need to directly test that the bidder isn't racially targeting with random test offers if it's a google style bot bidding system. A similar system is probably needed for political ads because one insidious fact of web targeted ads is there's much less chance to respond to and potentially debunk them if they're highly targeted. With radio and television ads you couldn't do that they'd go to everyone watching so more people outside the targeted demo would see.