If it is in good shape and you are upgrading to the iPhone 7, I would suggest taking advantage of the free iPhone 7 promo with Verizon. I think a couple other carriers have this promo as well but I have Verizon. Free 32 gb iPhone 7 or $650 off your iPhone 7 128 or 256 gb with the trade in of the iPhone 6, 6 plus, 6s or 6s plus. Check it out at Verizon.
Oh and for the Verizon suggestion, I am in Canada so selling old phone and using profit to buy the new one.