Most shops on used guns will offer %60 of their cost. So if a Glock cost them 440 to buy new they will offer up to 275 or maybe 300 any extra accessories mean nothing to them, they MIGHT give 10 per extra mag. Then they will put it on the shelf at their cost....440, and haggle from there. You talk then down to 400, you think you got a good deal, which you did, but they still made 100 to pay for lights and such.