See here (adsense example, each file is different in that directory). You can slightly change the logic in this code to only show ads to users above a certain trust level or user group (instead of below), etc.
FYI (and a hint)
./discourse-adplugin/assets/javascripts/discourse/components
This “may” be easily modified and rebuilt (test on your favorite staging server) to accomplish what you asked for, as I understood your original post (show ads to members only). If you based it on trust level or user group, then of course it is nearly trivial to modify.
Sorry, I have not tested, only looking into the code for you.