It doesn't have to be super accurate or super certain, for advertisers to catch a general trend. Even if the price adjustments lag significantly behind the act

It doesn't have to be super accurate or super certain, for advertisers to catch a general trend. Even if the price adjustments lag significantly behind the actual decrease in effectiveness - the loss of effectiveness will still drive down prices. As for personalized ads - I think the worst is still to come. Right now, most it is just about looking at a person's profile to decide which ad to show to them. But we are getting close to ML being used to actually create individual ads, optimized for each respective viewer.