As above if it already has a shiny new turbo I would be worried. But the golden rule is see if the injector have leaked I.e black tar like substance around the base of the injectors. If so walk away. The amount of crap inside the engine is a bitch to clean out to prevent future (soon) turbo failures.
I.e x3 oil and filter changes after vac pump removed and cleaned, sump and oil pump removed, oil pump strip and clean out, rocker cover off and clean and turbo oil feed and return replacement.
I’ve just finished a c4 1.6 HDI rebuild last night I intend to keep for my self so if any wants my old pug 307 sw 110 HDI (2.0L motor rebuilt and solid flywheel converted) give me a shout.