This thread prompted me to see what Gazelle would offer for a 64 GB Xs, and it's only $397, which is ridiculously low I feel, even for a trade in; less than 40% on a phone that is still the current model and not even 12 months old yet. I mean at that point, you're better off turning it back in to your carrier at the halfway point, since that's at least effectively $500.
Anyway, I can never sell an old one before I get a new one. I set every phone up as new, never restore from a backup, and want to match every single setting between phones, so this means holding the old phone in my left hand, new phone in my right hand, and painstakingly going through every single menu in each phone and setting them to be the same.