Every ad system I tried resulted in nearly 100% bot traffic to my site. Google and LinkedIn give you "tools" that will show you various numbers, but I implemented my own conversion tracking, because I didn't trust their numbers.

I decided to stop burning money on these ad systems. I'm not sure if they work for anyone at this point, I'm guessing this is more of everybody being convinced they might work and trying to get them to work, rather than ads actually resulting in conversions.

Well, I guess this might be different if you are an online casino or something similar.