[kamesama980]

In just the right situation maybe. 99% of the time, no. Depends on the scanner and what's wrong with the car.

Simply knowing the code isn't hard, just stop by autozone on the test drive and have them scan it.

No scanner can find a code that's been cleared. If the battery cables are removed or the codes are cleared, it's all gone. If the battery goes flat sitting on the lot, codes are gone. It cannot tell you the "history" of the car.

All the really useful data (fuel trims, live data, etc) won't be accessible unless you have a moderately expensive scanner...$200+ for a basic handheld one.

99% of the time, you won't find anything conclusive. Even if you do notice something like the fuel trims being high you can't do much about it since it isn't your car. you *may* be able to get some negotiation room but it's doubtful it'll offset the cost of a scanner to get fuel trims. The seller also might just give you the finger.