What do you consider high mileage when purching a 2nd hand car?

It also depends on the car regarding the mileage as some cars can do massive mileage without issue. What ones are you looking at?

200 k km is about max I would go when buying a car of that value and it would want to be a car known for reliability and have been serviced regularly. Sometimes the price difference between average and high miles isn't worth it due to potential big bills but more importantly resale. If you buy a high mileage car and then put up a decent amount of kms then you will struggle to sell a very high mileage car . If you did say 12 k km a year a high mileage car might make sense

You are hardly seeing aload of petrol models with all that mileage on them at that price ?

I used to buy 3 year old VW Golf's and Passat's with over 150,000 miles from the UK for about €6,500 or so. They always had full main dealer service history and 1 owner. Never had an issue with them.

with 600k kms and on its first replacement set of front brake pads

You have 600k on a car that is only on it's second set of brake pads?

Better look for where and how car was used and serviced rather than the mileage.
Hatchbacks of your choice may have been raced, but may be in a hands of careful commuter. Or someone carrying friends for gigs regularly. Generally overall condition very indicative of the previous owner. Unless the car has been restored and prepared.

Scratched up and neglected boot and door panels for example are red flags often. Pop the bonnet and you see a mess there. Walk away don’t look further.

Yes 1.5 dci 86 bhp Megane mk3. i don't notice any oil use between changes which are at 20k kms. It takes cheap 5w40 oil, doesn't need to be low SAPS as the car has no DPF.

I suck the oil out and as the filter can be accessed from above, oil changes are dead easy and dont need the car to be raised. 2009 to 2010 is the sweetspot as from 2011 on they got a DPF. Renault put a lot of effort into the reliability of the Mk3 due to the poor reputation of the Mk2.

Clearly mine is a high mileage car and has done a lot of long journeys. Easy on the engine. For a car that does lower mileage/short journeys, I'd probably recommend 10k oil changes, especially since the oil is cheap and so easy to change.

On carzone cars with 400k+ are 0.05% of the cars for sale.

Cars don't normally get to those mileages because the cost of repairs and maintenance doesn't make economic sense.

At around the 80-100k point is around the point most cars have a very expensive service intervals and that impacts ownership costs. The higher the mileage the more often other things start to go. Door locks, window motors, fuel pumps, suspension, seats sagging.

I know one guy who has his cars on finance and changes them before first NCT. He never even changes the tyres. He pays extra for this, but think of the time he saves.

Also modern cars have become very expensive to repair. Parts are expensive and in short supply. I've an older car with I dunno about 170k. But that's city miles and it does low annual mileage. At the moment one door lock is failing. I've already replaced two and one window motor. We've had cars taxis with 400k on them and they drove like a couch you got out of skip.

Modern cars can do far higher miles than cars used to but they are becoming very expensive to repair. One careful driver doing massive motorway miles might get longer out of car. But that doesn't mean that's what everyone else is doing.

I've changed cars because they had high running costs, repair costs, or they just didn't suit any more, too small, too slow etc. If someone doing the same thing for 300k then they might keep a car longer. But other people might have changed circumstances so their driving requirements have changed.

It comes down to how the car was maintained and serviced i.e. a high mileage car regularly serviced at the required intervals is much better then a car with low mileage but neglected.