Checklist to verify a used Rolex Submariner before buying

I’m Pedro — skeptical, technical, and I don’t trust sellers. Looking at a used Rolex Submariner (no papers). Before I pay anything, what are the concrete, low-risk checks I can do myself and which things need a watchmaker? My specific questions:

– Where to find the serial/reference depending on year (between lugs vs rehaut) and what exact formats to expect for 5-digit refs (examples welcome).
– What movement calibres are common for Submariner lines (which years use 3135 vs 3235) and how to verify the calibre without opening the case myself.
– Simple functional checks: bezel clicks (should be unidirectional, ~120 clicks), smooth screw-down crown action, date alignment and quickset, cyclops magnification (~2.5x expected), lume behaviour in darkness.
– Weight and dimensions: reasonable tolerances vs obvious fakes; endlink/bracelet fit and common fake giveaways (bracelet stretch, sloppy endlinks, wrong clasp code).
– Timing expectations: realistic accuracy for a serviced Submariner (Rolex spec vs real world) and what to expect if it hasn’t been serviced in years.
– Which tests require a watchmaker: pressure test for 300m rating, opening to verify movement and serials, and swapping parts detection.
– Immediate red flags that should make me walk away.

Keep it technical and practical — I want a concise checklist I can run through at purchase and a short list of things to request from the seller or confirm at a shop.