Whilst i agree with the rest of your post i dont entirely agree with this statmement.
YES, there are many shonky people out there tying to squeeze extra dollars out of you in the sale by winding down K's but there are also alot of people who legitemately only do 6,000k's a year on their cars and keep them strictly for weekend cruises and take maticulate care of their vehicle at all times.
I was in the GTR market for about 7-8 months before i found mine and I can tell you the windback jobs where very evident. I saw 34 GTR's with completely worn gear knobs, seats, steering wheels and in general crappy condition and the ODO on their pretty Nismo 320kmh dash reads "47,000". Heck my daily has 170,000 on the clock (highway km's) and if I where to cover the ODO and make people guess I would give $50 to anyone who said it was over 100,000km's.
At the end you dont know what the cars been through unless your its first and only owner /thread.