Cross-listing is the easy half. Put a jacket on four marketplaces and you have four times the eyes on it. You also have four ways to sell the same jacket to four different people, and three of those conversations end with you apologizing.
So the part of Arck that actually earns the subscription is not the publishing. It is the delisting.
The chain
When an item sells, one event kicks off a fan-out: every other marketplace that item is live on gets a delist queued for it, each one runs independently, and the sale is only marked complete once all of them have reported back.
That last clause is doing more work than it looks like. A pipeline that queues four delists and calls itself done is a pipeline that quietly leaves the jacket up on Depop. Every hop has to close.
Why some are instant and some are not
Marketplaces that expose a delist API come down in seconds. The others have no such thing, so Arck takes them down through your own signed-in browser session, which means that half needs your browser open. It is the same constraint that makes publishing scheduled rather than instant, and it is not a limitation we can engineer around from a server.
What you see
One notification when the whole fan-out is finished, not four. And when a delist fails, it says which platform and why, because a failure that does not name itself is a failure you get to diagnose from scratch three weeks later.