Whilst I agree with your coments regarding caution on posting this information, the professional crooks will already know a way to do it, its us as future prchasers who need to know what to look for, in the old days it was mis-aligned digits, scratches on screws etc, what do we look for now?
That would be the answer I'd like to know.
Forget about complicated things like electronic recorders, which may not be present, but which you do not know where they are or how to read them.
As usual the answer is much easier.
The state of the vehicle. Twist grip rubbers. Foot rest rubbers (if fitted). Bar ends. Mirrors. Scratches on screen. Scratches on bodywork and metal work. The dreaded rust. Worn disks.
In short, does it look like it's done 50k, 30k, 20k or the 9k the vendor claims? Compare it with other bikes you have seen, known or owned. If you doubt it, chances are you are right...walk away.
The service records. OK they can be written in and have fake stamps, or the owner could have done (or not done) their own servicing. But earlier owners (if applicaccable) are possibly reasonably honest. Most BuMW garages hold the service records for several years, they will have recorded the mileage, see if it matches by simply ringing the dealer up. Again, if you have any doubt, walk.
MOT records, if the pass sheets were kept.
IN SHORT: DOES IT ALL SMELL RIGHT?
IF IN DOUBT: DON'T BUY IT OR THEN CLAIM YOU WERE RIPPED OFF. THERE ARE HUNDREDS OF GOOD BIKES OUT THERE BUT JUST A VERY FEW REAL BARGAINS.