I gave Gazelle a try, having read good reviews. The first iphone6 phone I received from Gazelle died in two days and wouldn't turn back on.
They took that back and sent me a second. The second one started deteriorating in battery life shortly after the 30 day warranty was up and within 90 days is hardly usable. I called customer service to see if there was anything they would do and they said they could not.
So if you are buying a used phone from them, it is probably advisable to expect it won't last long. I'm back to only buying new phones from carriers in the future.
Review about: Apple Iphone 6 Cell Phone.
Reason of review: Bad quality.