It would be a third party tool, with code that is pasted into a listing description. l don't know of any personally, but it will probably have the name of whoever developed it somewhere on the window that displays the FB comments in listings.
It's geared more towards item specifc feedback so buyers don't have to sift through a profile for comments relating to an item they're interested in, but it looks like there's some other options (not free, though there is a 30-day trial). Most of the others I saw from a quick google search were for putting eBay feedback on independent websites and wouldn't work on eBay, but a more refined or thorough search will probably turn up what you're looking for.
