Tough one. I like the idea of creating /r/ads as a safe space for advertisers. Aside from that though, I'd leave it up to individual subs. As you have most of the big subs, for that I'd recommend an "Ad" flair/tag, so that you are calling them out but not censoring/removing. I guess in another system you could move all ads to /r/ads, but you can't really move content here.

Maybe spam/high volume ads is another use case where we should ban and delete the posts.

I do think voting solves this mostly although maybe that changes if downvote goes away.