In general, A/B testing is studying the website. You're not testing us, you're testing the best ways to convince us to do stuff. On top of that, when users visit your website (which is presumably pitching something to them), they know they're being pitched. They know the website is going to try to convince them to do stuff--click over here, watch this video, sign up for foogadgetmcawesome. Same drill with advertising. Yeah, this commercial with the freaking Budweiser puppy made me cr--er, chop onions--in its attempt to get me to buy beer, but I know they're trying to sell me beer, and I knew as soon as the puppy hit the screen that I'd probably start sniffling.