I must admit, whilst I didn't want to say it, I am inclined to agree. The lowest mileage petrol Octavia I found on AutoTrader (UK car selling site) for your budget of c. £7500, with full service history, had 70k on it (112,000km) which isn't exactly low. It was also pretty bare bones and had the 1.0 in it, which won't get you anywhere all that fast.
Most appropriate thing was something like this
@maxroal I have been in your position. For my first car, I bought a very clean 2013 1.0 Focus. From a small backstreet garage in the Midlands, it had 55,000km on it, one owner and cost me 7200 euros. It was very clean, and everything checked out. Fast forward three months and it had virtually blown up, with a repair list in the thousands. Turns out it was a lemon, with an engine and gearbox from a different car. I managed to get rid of it for under half of what I had paid, and promptly emptied my bank account at a SEAT dealer.
Anyway, my point is - if you don't know all that much about cars, while it is unlikely, you could run into the same issues I had. It might be worth waiting a while, or reconsidering things, and seeing what a main dealer could do a Fabia or something for. The last thing you want is to be thousands into a car that is nothing but trouble.