Many garages (and i don't say all) buy cars at auction, warrant them with the RAC etc, and call it a good job. There's no particular checking before they go out.
Modern cars however, are pretty reliable on the whole, so you tend to only end up with a real disaster every now and again. Thus the variability in some reviews!
The best way to stack those odds in your favour (and this is only my two penneth):
Avoid diesel, generally. They are more complex than petrol, with DPFs in the exhaust that clog, and turbo's on the engines that can fail.
Japanese cars are generally more reliable. Think Mazda, Honda, Toyota, with the last two of those being the halo's. (Nissan have a big tie in with Renault, and are okay on reliability, rather than good).
Non-turbo petrol cars from the above have the least to go wrong, and generally present a decent bet. In my extended family there are two honda civics (152k miles on one, 79k on the other) which present no problems at all. There's also a mazda 2 (120k miles) which I'm taking on a 1000 mile round trip to Scotland in a weeks time, such is my confidence in it.
You don't state a budget per se, but the above can be had in a reasonable price bracket.
Last bit of what is now quite a long ramble; Service history, with oil changes at least every 10k miles shows a car that's been respectfully used. In my very very humble, i'd have a higher mileague car with an excellent service history than a lower mileague one with a bad one.
Similarly, a car with good quality tyres is generally one that hasn't been subject to a very tight budget.
Last thing, promise. When you drive the car, make sure there aren't any suspicious knocks or clonks, that the clutch engages smoothly, and that the gears all slot in as they should. You can also check the state of the engine very crudely, by removing the oil cap from under the bonnet before you drive. If there's any 'mayo coloured' gunk on the cap, it can be a sign of a head gasket failure, and chunky repair bills!
Sorry this was so long! Good luck with however it goes.