As others have said the last place you want to sell a gun is a dealer.He will always offer you the least amount of all the other ways to sell it.Worked it retail gun sales many years ago, customer brings in guns,two or three salesmen add up what low retail would be and they take the average and offer 50%.
Only works for divorce's,widows and heirs when they don't care as they have no money in it.
If you want to sell a gun do it yourself.If that was my gun I would first try on here after looking what they typically sell for,not what they offered at and most certainly not retail.