Just like new
There are a lot of Police trade ins and used firearms out there that can be purchased and 30%-40% below what NEW prices are. There are a few online FFL dealers that pick up the police issued Glocks and Sigs and resell them for under $400. I picked up a few that had a lot of holster wear but once I opened the action, they were hardly fired and they ran flawlessy. Most of the time this is the type of condition most Police trade ins are found.
Some firearms may have actually been shot a lot, but if you think the accuracy in your Glock is starting to deteriorate, if you got it at a good price in the first place, replacing the barrel is easy and not a headache. Most of the type a barrel will just drop right in. Glock Barrels can be found for under $200 and will last longer than most shooters will ever know.