In addition to Facebook groups and FB Marketplace there's also Craigslist, OfferUp, and LetGo. FB groups are a more targeted, curated audience and has the transparency advantage because most people aren't anonymous. But you're also subject to the group owner's rules and whims. FBM has a less targeted audience but does provide you page views so you can at least get a sense of the traffic. I've found that FBM traffic is comparable to or better than eBay.
CL, OU, and LG are a step above the Wild West.
In general, buyers on those platforms are less likely to make impulse purchases compared to AZ and EB. They're more likely to be looking for a bargain, so you can expect them to offer 25-50% below your asking price.