Typically speaking, a VW with 50,000 miles on is barely run in...
Not really true of
mine of course, but it did have a rather unfortunate life history ... nothing but shopping trips followed by nothing but full throttle abuse.
Something of that age with that mileage is not very much over what I last remember being the national average anyway - though I first had a 12 year old car with 54k miles, and moved on to one 8 years old with 29k, I don't think I'd be too happy touching a very low mileage one. Certainly not as low as the polo was, without assurance that it was because of low usage, rather than frequent but very short trips. (With the astra, I had that assurance and fair proof of it... the polo, i didn't!)
As everyone else has said - one that's seen a fair bit of use haring up and down motorways at 70-80-90mph for 12,000 miles a year - so long as it was largely in high gear without lots of very wide throttle - should be far more capable of carrying on for yonks than one that's done 6,000 a year going 10 miles or less on every trip (barely getting warm) and seen lots of stop-go strain, or worse been used on delivery runs (i.e. regularly HAMMERED from cold).
Additionally, the high miler is more likely to have been well serviced and had attention paid to it - someone having to drive for their job like that would be a fool to not at least pay passing attention to their oil, tyres, any funny feelings or noises etc. Not to say that they wouldn't, as there's a lot of fools, but statistics are on your side.
In the days when gearing was quite short and engine outputs low, with bad aerodynamics and parts seemingly made of pewter grade material, a high mileage car would be a banger simply because the engine, transmission and ancillaries would be knackered, but these days one that can't make it through to 120, 150 thousand has been badly looked after (200 or more for truly cosseted or motorway-slog-only examples). That's why odometers have a sixth number now!
Not to mention the bodywork lasts nearly forever compared to even early 80s cars.
There probably are a few VW & Polo specific problems that you may want to look for in something that's over 50k, but I don't think I'm the best one to explain them. Best bets are, as ever:
Cambelt (& alternator belt)
Gearbox
Signs of severe abuse from engine
Maybe wheel bearings, exhaust, HT leads, brake components etc - perishable but fairly long life items
Check the oil, coolant, brake fluid, other replacables are in good fettle, and the tyres too. If they're neglected, perhaps the whole car was too. Beware the motor that only EVER gets attention at the annual service.
Arch rust and rust in any other vulnerable places. If it gets on the sills or other load bearing parts you're still screwed, but that's super rare now, particularly in something under 15 years old.
But didn't want to give insurance the satisfaction of chargin me 1800 for just 3rd party fire n theft lol