With modern cars, even the least reliable makes and models don't all fail. If someone has had a car with faultless reliability for 10 years, you now can't buy the same model.
If you just work from your own experience, or that of personal contacts, you don't get a big enough sample size to judge. Sites like
www.whatcar.com and the car-by-car breakdown at
www.honestjohn.co.uk let you feedback from a bigger sample. When you look at customer satisfaction surveys, you sometimes need to be careful to filter the reviews. Some people are satisfied because they expected poor customer service and it was adequate. Others are dissatisfied when the service was only excellent and they expected more. Owners of a Morris Minor will tell you how their car is perfectly reliable, neglecting to mention routine maintenence they have to do every month. There are other people who expect to fill a car with fuel and do nothing else.
Sometimes there are problems with a specific model which can take time to appear. In the first couple of years when a model of car is produced, they tend to have a lot of minor problems. The worst problems will be fixed with a recall. With others, they might correct the problem on the new cars, and leave the owners of the ones that have already been sold to sort out the problems for themselves.
If you get an unusual car, then you may end up paying for a mechanic to work out the foibles. If its a common car, then hopefully they will have already learnt the tricks when someone else was paying. If you get a niche model, make sure you have easy access to a garage or mechanic with experience of working with them.
Big complicated cars depreciate faster than small ones. Running costs on a bigger car are not that much more, but when stuff goes wrong, everything is more expensive, and with a higher specification, there is more to go wrong. Premium brands like Audi depreciate slower than mass market ones. If you sell a car when its still new, then depreciation will be a big part of the amount that you pay.
If you buy a second hand car, and can get one from someone that you trust, who is selling it for a good reason, then that helps to reduce the chances of getting a bad car. Some people sell their car because they are bored or it, or its too big or too small, then that is fine. If they know its about to need expensive repairs, or they can't afford the running costs and haven't bothered to service it, then its one to avoid.
