Have you integrated account age into the course recommendation service? I imagine newer accounts (potentially newer developers) would have higher click-through rates than older accounts (probably seasoned developers) and if that’s true then you can increase the value of the course providers’ ad spend a bit.

Likewise, you might be able to somehow classify how “elementary” a stack overflow question is and use that as an input into whether or not to serve a course ad. The idea being that viewers of “simpler” topics (e.g. “what is the difference between const and let in javascript?”) would be more likely to pursue a course than say viewers of more “difficult” topics (e.g. “why doesn’t WeakMap support Symbols as keys?”). That’d be a cool classification project, perhaps someone at SO already has a method for this that you can borrow.