if you're wearly of bidding cams and stuff, bring a CR123A and a LR44 cell to your nearest pawn shop or goodwill and look for them.
Check the optics first, the lens from front, is it good and clear, no scratch.
2. open the back of the cam (if there's a tab on bottom left of camera, pull), if not, pull up the film rewind. Is the back clean? Is it super moldy?
3. keep it open, turn aperture dial to 1.7, point cam to a light, cock shutter and fire. Do you see an image projected?
4. repeat 3 a few more times, does the timing seem consistent (should be 1/500s without a battery).
5. look inside the VF, is it hazy, can you focus, trying focusing a light, then some brown things.
6. stick up your finger while looking into VF, block the focus patch area with your finger in front of the VF, is the yellow AUX patch clear? is it broken? shaved?
7. if you wear glasses, peek into VF without glasses, is the diamond nice?
more. Stick in your CR123A battery + LR44, positive pointing OUT. Close lid.
8. press battery check, is there a light?
9. while the back's opened, look at lens. Turn aperture ring to 1.7, turn shutter ring to B. cock fire and hold. any defects in the optics? Does it open wide?
10. while holding the B, turn aperture ring, do the blades snaps nice? Any oil, scratches?
11. turn shutter ring to flash. cock and fire, repeat, does it sound consistent (1/30s).
12. turn ring back to AUTO.
13. turn A ring to 16, iso to 100, cock and fire. Do you hear a little whiz before the shutter closes?
14. adjust iso ring, does the shutter compensate timings?
15. keep iso at constant, adjust A ring, does shutter compensate? Are they consistent?
16. forget about the light seal foam, you can fix that DIY or anywhere, cheap.
17. close camera back, does the counter reset to S?
18. is the filter ring dented? bring your own 55mm UV to check.
19. everyone knows, does it clunk when you cock, trivial, first thing you check anyway.
When I was buying mine I didn't know anything. But I bought from a good source and it costed me $110. worths every penny. If any of the conditions above doesn't meet, skip it, go find another one. the repair usually out-cost the purchase. Get a good one to start with man and it'll reward you with some nice bokehs 🙂