Can someone use eBay as an intermediary when they list on a different platform?

[disneyshopper]

What do you mean by "intermediary"?  If you list an item on another platform and it sells, you are responsible for shipping that item to the buyer.  ebay would have nothing to do with that sale.  If you list the item on ebay, and it sells, you are responsible for shipping the item to the buyer.

[evry1nositswindy]

Are you looking at a vehicle/mower/ATV on another site and it says the payment will be handled through eBay?  This is a SCAM.  Don't fall for it and report the listing to whatever site you found it on.  NO, eBay does not work this way.

[rock.star]

Scam!  EBay has nothing to do with anything you may see on some other website!