Try the Facebook marketplace as it is local and very effective. I’ve sold through it before. There’s Also an app called LetGo for selling or buying things, and I also recommend the NextDoor neighbourhood app. If you care to know about any of these do let me know. I sold my 6s Plus but I really enjoyed having it. Oh there’s also Gazelle for selling and buying used mobile phones, laptops, iPads, etc.
Hope that helps. You’ve probably found one by now!
Georgia Cheer
CeX is also good. They have shops in many places now (or online) and they offer a two year warranty on secondhand units. They're not rock-bottom prices of course but still reasonable.
Gillian Perrott 