As this project appears to be fairly unknown in the fediverse still, I’d like to use this opportunity to advertise Flohmarkt. This Fediverse equivalent of Facebook Marketplace already has some instances up and running - see here: https://codeberg.org/flohmarkt/flohmarkt/wiki/flohmarkt-instances
I tried to use it myself and it really isn’t ready yet. It’s missing so many features that a specialized Lemmy instance seems like a much better alternative.
Maybe share your vision with the devs or actively contribute yourself to the development of this platform? :)