I do not think that the ad companies like Google and Amazon are all that good at targeting their ads. I do a search for something, like a lathe and bingo, I suddenly see a bunch of ads for lathes. All kinds of lathes.
As I read this thread, I saw an add on the right for a digital caliper and it was an Amazon ad; it said so. So, is that ad on this page because of your post? Or was that Amazon caliper ad there because you posted here?
Either way, I am not sure how that works. If you are being targeted with ads for calipers, why am I seeing it. I have not done any searches for calipers or viewed any pages about them lately. So it seems unlikely that I am seeing it because you were looking at them. Perhaps they are just reacting to your post which contained those two words, "Amazon" and "caliper". Whatever they are doing, it really is not a very good or intelligent use of the massive files that they keep on all of us.
I have worked for ad agencies and my personal opinion is they really don't have a clue. When their techniques work it is more due to having a good product and some luck than to any skill at selling things on their part. One thing an ad agency will never, EVER do is let themselves be paid on a per sale basis. Never! They would go broke.
Don't believe me? Well the OWNER of an ad company I worked for actually stated that only one in ten of their ad campaigns actually sold enough product to pay for the campaign. The other nine were at a loss for the client companies. So just how good can they be at selling something? What they are good at is moving money from someone else's pocket to theirs.
A few ads aren't targeted to me, but the Amazon calipers ad definitely is.