I currently run a few different Facebook pages, and when I go to post something on Facebook Marketplace, I'm given the option of posting as those pages:
However these are not all the pages I run. In fact, these two pages relate to a mobile app I've written, primarily targeted at people outside of Australia, so I'd never actually sell anything from those pages.
But now I've started up a new page for a hobby of mine (selling retro gaming stuff) and want to sell things to people in the local area. However, as shown in the screenshot, the page I want, doesn't actually appear.
EDIT: As I've only just recently started my page, I only have one like (myself). I was wondering if you have to reach a certain amount of likes before your page shows up, but I just added another page I'm an admin of, which has ~2,000 likes, to Facebook Business and it doesn't show up.