If you don't want to do the hard work, selling to FP and the likes is easy because you just need to wait to get paid once they receive your item. Yes there's a high possibility of getting a low-ball offer but sometimes they make a good offer. Even if your item is pristine, don't expect to receive a close to retail offer. They are a business and they have an overhead to account for. All the items I sent to FP were new and pristine and I still lost a good percentage but payout was guaranteed. One duplicate item I sold to FP actually got me $250 more than retail and I was really surprised.
As for selling in FB groups, always use PayPal invoicing NOT Friends & Family. PayPal invoicing gives you seller protection because the item is sold as a business transaction and they also charge you a small fee. If you do Friends & Family, there's no PayPal fee but there's also no seller protection so if someone vicious is scamming you, you'll be out of money and/or the item.
Do what's best for you and be careful if you're selling on your own