So you reckon all the speedo's have been wound back?
honestly theres to many skylines out the with 90,000 to 150,00km and there 15yo.
I dont know no-one is honest these days.
i would compare the km's to the actual wear and tear of the car and see if it matches up,leaks,compression,ect.
and if its been thrashed you would go to test drive it and it would run like a dog and have sounds banging outta of it i would assume.