Detect usage patterns of normal users vs these, and then block access. Ultimately comes down to the companies' ability to throw however many devs at thwarting this one as makes sense for them.

Just as an example I remember, Facebook sponsored posts would be labeled, but if you dug into the HTML, what you'd get was random permutations or junk added to the label, like SSpoSnoSsorReD or something, and they'd use complicated overlays or other things to get the label to be visible. So you wouldn't just be able to use a simple easy rule.