WE are definitely being constantly manipulated, and online it is more specifically targeted than, say, mainstream news, which tries to cater to the lowest common denominator. I try to notice it, but as you say, I'm sure I'm affected at least a little.
I think we all are at least a little. Even those trained to see, normally only see what they have been trained to look for. Perhaps rather than looking for the manipulators, we should look at the changes in our own behaviour instead. Understand that and the manipulations become transparent.