Theres already a million threads on SAU (some stickied) that talk about these things when buying a skyline, a 2 minute search will find them for you.
The only way to get true and believable genuine km's is to buy it brand new. If youre picking it up second hand, the next best thing would be to buy one with log books. A log booked car will always be more expensive though, at times up to 50 - 100% more... and rightly so. You are paying for the knowledge that your car probably hasnt been fiddled around with.
If you go for one without books then you are playing the russian roulette equivalent game known as importing a car. If you dont like the rules, dont play the game. You're not the first to feel hard done by, and certainly wont be the last.