Are you thinking on running it in a private relay or using the current public infrastructure?
I can see relay operators not being happy about providing infrastructure for it when people starts to sell goods/services that are controlled or outright illegal in their jurisdiction.
And if you're running it in a private relay, then you'll be responsible to moderate it or face possible legal repercussions down the (silk) road.
No one can moderate it. It will broadcast these events to all the known relays around the world.
It will function as a client for the marketplace, similar to other social clients. It has different event kind, relays can choose to block for themselves if they desire. But it will broadcast on its end.
If you broadcast to all relays, relays will need to moderate it - either block it or remove unwanted content . They may choose to block/remove only notes containing unwanted goods/services, or, more likely IMHO, just block these event types for simplicity. Otherwise, they'll risk prosecution.
I don't see a compelling reason for operators to host notes advertising, say drugs, guns, hitman's services, and risk being prosecuted, while at the same time getting no benefit from hosting them.
