Instead, it is a way to fool rational people - for example, Bayesians who update based on evidence will update wrong if fed biased evidence. Which doesn't really fit here.

It should be noted that it is a way to fool Bayesians over whom you have some kind of epistemic advantage. That is, you have to be for some reason better able to provide deceptive data than they are at accounting for your ability or inclination to deceive. That is hard to do without an overwhelming advantage in one of intelligence, power, knowledge or anonymity.

Another way to take advantage of confirmation bias is exemplified by horoscopes: offering people predictions that are sufficiently vague that no matter what happens, people can find a way to interpret the prediction as having come true.

Also, someone who wanted to be respected by many people could write semi-nuanced opinion texts that could be plausibly interpreted to favor either side in a debate. In the "best" case, supporters of both sides will read the text and like you for being on their side.

The way to actually use confirmation bias to convince people of things is to present beliefs you want to transmit to them as evidence for things they already believe. Then confirmation bias will lead them to believe this new evidence without question, because they wish to believe it to confirm their existing beliefs.

Yep. This works pretty well, too. Useful phrases: "As you already know ..." "... and you know all this already" "I haven't told you anything you didn't know already".