Can you share a link to an example? I've been using reddit for a decade, I've never seen anything so blatant (unless it's a sub dedicated to a specific product).

I can’t find one now, but it was in the e-commerce merchant space, promoting a Shopify app. I thought “interesting”, I hadn’t thought of it before.

I think most people who run sub-reddits don't make meaningful income from the platform. Yes, one could advertise certain things, but it is rarer in larger communities.