The low mileage = better and high mileage = worse myths exist to keep people buying new cars.
100,000km is not high mileage. Nor is 150,000km. Nor is 200,000km, because a maintained car can easily do hundreds of thousands of kilometres.
@OP:
The idea is to know the best point at which to sell, in order to lose less money, so you have more to spend on something newer. Sell at 150,000km. Depreciation rockets from then onwards.
Paranoid people won't buy over 100,000km, and combined with service/maintenance plan expiring, at 100,000km the car has suffered most of its depreciation. 150,000km is the next psychological mark. Sensible people tend to buy between 100,000km and 150,000km. By keeping it till 200,000km you'll get a lot less and you'll also struggle to sell.