I see hardly any ads at all on this site, even though my browser's ad blocker is disabled. (There are no ads at all as I'm typing this). What I do occasionally see though are a mixture of perfectly legitimate ads and some very dodgy-looking ones.
For example, I had a pop-up at the foot of my screen earlier this evening, advertising the University of Suffolk (which is based just a few miles down the road from me). I'm delighted that one of the newest universities in the country, which has received lots of praise for its courses and its standards, is getting some publicity. However the University's ad has replaced one that I've been seeing for the past week or so in the same position, inviting people to give their opinions in response to a question about Boris Johnson (which was phrased in meaningless gibberish anyway) in the hope of winning a prize. I avoided that one like the plague!