If you allow artists to display their work in various communities along with the ability to post links in their profiles, but you restrict actual posts to disallow self-promotion, it's the best of both worlds, IMO.

In other words, if you can't include self-promotion in your community posts, but everyone knows you have the links in your profile, it attracts less grifters and keeps the feed clean, while allowing anyone interested to contact a poster directly or ask them promotional questions via DMs.

That said, hosting a full-fledged marketplace is not a good idea, IMO. There are laws and banks involved, which mean lawyers and taxes, and volunteer management does not work for that. There are already marketplaces that do that well, and allowing artists to post their own links of choice in their profiles will let them steer actual business to other platforms, while keeping the fediverse for display, review, share and critique. My opinion, anyway.

After seeing your post on akkoma, I think I understand your point even better.
I want to support artists and would definitely buy music on fedi. I would rather just watch hobbyist make videos for peertube and especially for loops. But if it means that it would help the platform stay afloat I am way more open to the idea of monetization beyond just donations.

Lemmy loves free labor and freedom washed exploitation. Not sure you'll find a lot of support here.

Part of the headache here is that this situation inherently props up a few monopolistic platforms, rather than allowing people to use whatever payment system is available in their own countries. Some of this can be worked around using cryptocurrencies – famously, the Mitra project leverages Monero for this very purpose, although I'm told it now can accept other forms of payment as well.

Hell yeah, I didn't know about Mitra. It sounds like it's a Patreon esque kind of deal with what the payments part is for.