I wonder if the scammer is using emails and passwords from a breach against Facebook to access "reputable" accounts and then posting marketplace listings.

FB has many scam adverts that get reported but never taken down, I know as I got scammed from 1 and the company is listed online as a fraudulant company, but FB just dont care as they make advert money.

When I was still using facebook ages ago, I repeatedly reported trivially fake accounts. Every single time they concluded the accounts are fine.