I have dealt with Gazelle.com
in the past and they have earned a "trustworthy" mark from me. The only reason I didn't use them this last time and went with Gadgyt.com
was that it was an older phone and they didn't want it.
ONE LESSON LEARNED ... I don't remember if Gazelle uses USPS First Class or Priority ... but if it is First Class or over $50, pay for the insurance yourself. That way, if it is lost or stolen, you still get paid.