Best FB group for buying selling second hand phones

Hey folks, could you please recommend a decent buy sell Facebook group not too littered with garbage where I might be able to buy from a private seller a second hand Samsung 5/6 or iPhone 5/6? I presume there are quite a few people wanting to upgrade to the never versions and are happy to let their old ones go for decent prices. By the way, what would the general ballpark for used prices for those models be? Thanks for any advice.