THEPorsche 911 has been around forever and most have been cherished by loving owners so that even though they might have been driven hard, they have also been properly serviced.
So rule number one is: never buy one without the full dealer or Porsche specialist service history.
Do that and they can be had for much less than you might think, with the very likely hope they will be reliable.
When most other cars from that era have already gone to the scrapyard, earlier 911s are still giving huge joy, having been rebuilt and restored by loving owners regardless of expense.
All of these earlier cars are now classics, and many later models are also sold as classics even though they could hardly be termed so by age.
911s are about as family friendly as a motorbike - in fact there are lots of downsides - if I could only think of them.
But opening one up on a good road is like the first day of the holidays to anyone who loves driving.
Even the lowest powered models will reel in the horizon like fish on a line, with a top speed of 178 miles an hour and a zero to 62mph sprint of just five seconds
This is one of the most involving and entertaining cars ever made and feels as stable at 130 miles an hour on the autobahn as it does parked outside the house.
The handling and road-holding are sublime on dry roads and later models have all the electronic aids to keep you on the tarmac in the wet too.
But be warned, the earlier cars do not have much if any modern safety gear and a rear engine and rear wheel drive can make for tail slides in the rain unless you drive with a gentle right foot.
The design has been improved and perfected time and again and the earlier classic models are just as great to drive.
It has been one of the supercars of every era since it was launched, well able to hold its own against the best of the rest.
Older models are very noisy but soundproofing is much better the nearer you get to the present day.
Comfort is good but those fitted with optional 20-inch wheels ride much less smoothly.
Equipment is quite sparse in lower order models, but will probably have been up-graded by previous owners. Many will have leather upholstery and aircon.
Bear in mind that all 911s are expensive to run, with group 50 insurance, 23mpg, expensive parts and expensive servicing.
Finally, as with any such expensive sportscar, if you can, pay an expert to give it the full once over to make as sure as you can that you're buying a good one.
Pay about Â£18,650 for an '07 07-reg 325bhp Carrera 2, or Â£27,500 for a '10 10-reg 320bhp Carrera 4 Tiptronic automatic. Earlier models are down to under Â£10,000.