I have a Canonet QL19 and it's nearly identical to my GIII QL17 (which seems to be everyone's favourite model of Canonet). The main differences that I can see seem to be:
- maximum f1.9 aperature vs. f1.7 for the GIII
- 45mm lens vs. 40mm lens for the GIII
- no battery check button & indicator
- no little window on the back that shows if the shutter is cocked
Everything else seems to be pretty much the same, although it's my understanding that the build quality of the lens is supposed to be slightly lower than the GIII QL17.
I think if you check for the usual issues that these cameras suffer from: sticky shutters, light meter broken, etc. and it checks out as good, then $40 AUD isn't a bad price. I just developed a test roll from the QL19 but haven't had a chance to scan anything in yet; I can post examples from the camera later if you'd like.
BTW, I'm assuming that you're talking about a
new Canonet QL19 rather than the older version of the
Canonet QL19. The newer model has a hot shoe on top for the flash and has a PC socket on the left-hand side of the camera, covered by a rotating plastic cover (the older version has a PC socket on the front).