At least Youtube and Facebook offer this feature. It's pretty standard. The problem is that a lot of their inventory is an inch wide and a mile deep. The rule

At least Youtube and Facebook offer this feature. It's pretty standard. The problem is that a lot of their inventory is an inch wide and a mile deep. The rule is roughly "narrow targeting, cheap impressions, reasonable frequency, pick any one". A shady ad agency (but I repeat myself) will never pick "reasonable frequency" because their advertisers aren't sophisticated enough to ask if their ad is being sent to one person 50 times in a day. It only takes one buyer to not set the frequency control option to spam you with the same ad over and over -- everyone else is one-and-done.