A mate of mine here in Australia recently moved apartment and wanted to flip a whole heap of her stuff (bed frame, lounges, etc.) to downsize. She was using gumtree (the traditional 'I need to sell a lounge/fridge/etc. site used here) but was getting pretty poor responses. She then tried FB Marketplace and found it to be a huge gain in both quantity of responses (~10x) and their quality (people weren't offering her like 20% of what she listed it at).
I also see many uni kids flipping their textbooks and other small belongings on it, because it's really easy and right there in the app everyone looks at all the time. It also targets location, so uni kids living on campus sell directly to other uni kids living on campus and so exchanges become trivially easy.
It may not have disrupted the US market, but it's certainly had an impact elsewhere.
