I wouldn't hope for a heck of a lot. It's like trading in your Chevy at the dealer. There is no shortage of used ones, so the demand isn't there. Of course, if you can sell it youself you will do better. Being Gen 4 may help some. $300 to $350 is what I would expect to see on offer. Maybe more, maybe less depending on the used Glock supply in your area. Note: I'm not in the used gun business, this is simply an educated guesstimate.