i would first check the spring in the magazine,if it has gotten weak it may be causing this,also clean the magazine tube out if your gunsmith didnt.i would also try some hotter shells and see if works with those.if these things fail i probably would want to get rid of it also.i would be honest with whoever is interested and let them know like you said,and try to agree on a price thats fair. but first i would try to fix it,something is causing this and more than likely it can be fixed,you could also contact the manufacturer and see what they say,it may be something simple and you dont want to take a loss and find out its something simple.try to get to the bottom of it before you decide to sell.