When buying, what mileage would you consider too much?

[AW8]

Just to add - contrary to an earlier post made here. No timing belts on any E53 models but plenty of other critical belts to consider as belt failure can have its own associated consequences.

As for petrol engines not failing - generally I would agree albeit I know of a couple of 4.6is models that had had issues needing engine rebuilds. Timing chains and guides worth keeping an eye (or ear) on too.