I would say if you cant sell it try and get the most the shop owner will give you on trade in.
Most of the shops I've been to will sell it for you, and then want 15% - I'd rather just hang onto it and keep it as a backup before going that route. I'll most likely hunt with it this year and see what I can get for it - even though I'm sure I'd get more if I sold it a few months before hunting season.