Dont worry im not going to judge you, dont have a high horse
Only way to really tell if the car is any good is to have a proper good look around it
Mileage is a good indicator but it isnt everything i personally would rather own a 90k car that has been looked after than a trashed 40k one
Service history too isnt everything bro, some people service themselves, minor services are easy to do
For around 6k you aint gonna be getting anything other than a DE engine, but thats fine, nothing wrong with them just a little less power
Youll get the general vibe when looking if your smart enough, check for things that indicate its well looked after, eg the tyres, if they are good tyres, its probably been looked after