Just thinking out loud about the Nostr marketplace idea... rather than have any kind of "submission" process, Nostrgram could just scan the relays for notes that have a certain hashtag (e.g. #marketplace) and that include any required information. Those notes would show up in a special feed that can be searched and filtered.

I really think that could work well, plus it prevents it from being client-specific. Any client could filter and search for notes with the same hashtag and organize the marketplace in their own way.