Well, you either get lucky, manipulate them, or get an inspection.
Whether that's you doing it, having the seller take it to a shop, paying a mechanic in the area to have a look, or finding someone you know here or otherwise to have a look and send you lots of pictures and fire it up with the phone in hand before test driving and recording any data the car will provide.
This is one of those times when on-board diagnostics can actually be a great convenience; especially if a dealer is nearby or someone has the computer. Your best friend will many times be one of those "147,000 Point Inspections". It may seem like they cover the obvious stuff, but it's the obvious stuff you'll chance forgetting.
If you're nice enough on the phone, you can often get the guy doing the checks to snap a few pictures of areas of interest and at least text them to you.
ABS is obvious stuff. If you weren't into Rovers and were staring at a used DII with no lights on the dash, you might never consider it; which would suck, because as we all know they can go a while before the Amigos show up after a reset. Other cars have their own quirks. Dealers are good for telling you all manner of horror stories whether they intend to or not.
In the end, you have to get eyes on the thing somehow or just roll the dice.
Don't forget, though, that a car says a lot about it's owner, and an owner's behavior typically does actually say a lot about the condition of the car. People that don't communicate are incapable of having maintained a vehicle. If they did, they'd have built up the skill, or would at least understand how important it is in life.
If you want a good car, don't buy it from someone that won't answer a clear question with a clear answer. Indeed, that's good advice for life in general. Don't deal with people who refuse to communicate properly. The result is nearly always negative.
Cheers,
Kennith
