using hashtag for marketing is already a thing on other social media platforms. nostr doesn't do that any better. in some ways it does it worse because there's so much clutter in hashtags that isn't filtered out by algorithms looking at content quality.
the ROI on social media marketing via ads is unbeatable right now. the money that you pay to get your small business to get it in front of exactly who your customer is cheap compared to other methods. The big SM sites can do it because they have so much user data.
How does Nostr beat that? Right now, I don't have an answer for that. Maybe inherent in it's decentralized design it can't. Maybe because of its decentralized design, it can.
I'm planning on running a Nostr only Bitcoin only small business so I'll let you know how it goes.