Heated seats and steering wheel (so effectively a "winter pack") has been standard on the GTI / CS since the MK 8.5 was launched.
I was being a little lazy about not ringing the dealer to check. Checked and rechecked the specifications and it isn't showing but there are so many to list that it could have just been overlooked.. Will have to make the trip over there if it ever stops raining and do a test drive. I seem to have a fear of visiting the dealership for some reason 😂.
If you’re relying on the content of a VW Approved Used car advert to be correct as far as the vehicle’s spec is concerned, be aware they’re often just a ‘cut and paste’ effort that can be littered with errors and omissions.
From my own personal experience, IMHO many car sales staff also have limited knowledge, so won’t always know - or be able to accurately confirm - the spec of the vehicles they're selling. The cynic in me would say that a time-served car sales person with a particular car brand who is an enthusiast with a comprehensive knowledge and a genuine love of the product they’re selling is a rare beast these days; many are only interested in hitting their sales targets to earn a sales bonus….

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Therefore, if you do your own research and pick the brains of forum members (as you are doing) before going to view the car you’re considering, it’ll make it easier for you to confirm yourself that it has all the standard equipment it should have and also what additional options it’s got.
Assuming you have an existing car to sell, it’s also worth doing your research on what it’s worth and the various options available to you for selling it - car buying services such as Motorway or Carwow might mean you get more for your car than you would trading it in against a replacement car at a car dealership.