I think you were trying to reply to me.

I'm not a web developer, and I don't do anything similar on my pages, blog posts, whatever, so I don't know.

The only non-predatory way to do this is to being honest/transparent and don't pulling tricks on people.

However, I think, A/B testing can be used in a non-predatory way in UI testing, by measuring negative comment between two new versions, assuming that you genuinely don't know which version is better for the users.