How does eBay know that the item has been sold if you don't mark it as Delivered nor the buyer mark it as Paid?
To me, it's a time-consuming task to go through eBay messaging for each and every one of the transaction, just to ensure there isn't any violation.
But for some reason, they do know; so once you cancel the ads or even leave it for sometime then cancel the ads, they will know.
but what i'm interested is .. how?
I think you're liable for the ebay fees, once the buyer clicks on 'buy' or 'wins' the auction. They don't really care if you mark it as shipped or the buyer marks it as paid.
Ebay try to block messages where you exchange contact details before the buyer has purchased the item, but it doesn't always work.