I own the following
Glock 21 police trade in when my brand new Glock 21sf was obsconded with by my wife.
Glock 23 that was in almost perfect condition
Glock 26 that was in good condition, I replaced the plastic recoil spring with a metal one, and slide lock lever today as a matter of fact.
I’ve purchased used before as well and ran into no problems, all were purchased from/through reputable FFLs I have purchased from before I’ve never had a problem.
I’ve inspected them checking for functionality and excessive wear. So far I experienced/found two issues I’ll explain.
The first police trade in G21 was brought out and during my inspection the slide lock lever just fell out of the frame when I turn the pistol to the side. 2nd one brought out was in better shape and had no issues, that’s the one I purchased and have owned ever since.
The G26 was a bit off with the action when racking the slide I found the recoil spring was not holding in place and would wiggle its way out of the barrel seat and bind inside the frame channel, I also found the slide lock lever was installed backwards causing the barrel lock lug to not catch the notch in the lock lever as it was backwards. It was also taking a bit more effort to pull down to allow disassembling as it seemed the ends were barely clearing the outside if the frame slot. After replacement of both it’s been running like a champ.