My local news has a classifieds section (free to list/post whatever you've got for sale). Sold my old pedal bike that way when I got an ebike a couple months ago.
As long as you're not shooting for absolute top dollar for them, a good option.
There's also a couple bike shops near me that'll either outright buy a bike off you and resell it, or use it for parts, or even sell on consignment. Neither were interested in my bike though, partly because I was selling it in August (end of the busy season for them).