I have used Gazelle before and didn't have a problem. This time they quoted me $180 for a phone. I ended up with 80. They said they downgraded the phone condition, but this phone looked barely used.
Avoid, there are other options. Also, you have to check your spam folder, apparently Gazelle gets sent there and if you don't check it you won't know you were downgraded and will have no recourse but to accept their decision. I would use another service.