Another "issue" is the Glock 19 is like the most popular handgun in the world so it holds value better than most. 

If you want cheap Glock, best bet is a police trade in glock22. They are less popular .40cal and full size instead of compact like 19. 

But there are millions of them because basically every PD in the US used them, then switched back to 9mm a few years ago and dumped them all cheap.