I once owned an ex-VW Press Fleet 2006 Polo GTI 1.8t.
It was still under factory warranty mind you so I had little concern about the mechanicals.
However the car was faultless (aside from giving me back ache).
Admittedly it was the uglier 5 door so wasn’t deemed sexy enough to feature in car magazine performance testing or road tests but I’m sure it had an interesting run in period!
It would be easy enough to email the journalist who ran it as a long termer to ask what sort of life it led.
Some long term cars are used for camera cars in action and track shots and some are just daily drivers for journos when they don’t have another road test car.
The versatility of a Golf GTI means it could be used for all sorts of jobs.
At least any early life faults will be documented unlike an ex lease vehicle which would have possibly had a similar start to life on the road. There are plenty of badly driven and uncared for privately owned cars around too.
Go with your gut feeling depending on the car’s general condition and how it drives after an extended run.
Compare it with a newer car and if it feels tired then walk away.