If you could convince a seller to allow you to have your mechanic remove a cylinder and have a good look inside, this would be the way to go.
Very few I suspect would agree to that, for many reasons, chief among them if there is something obviously wrong....
Pulling a jug to inspect an O-200 as part of a pre-purchase would be very wrong. Doing so would unnecessarily reduce the reliability of the engine and, as a seller, I would expect financial compensation from a potential buyer who did this. There's no need to perform exploratory surgery when less invasive means are available to understand engine health.
Go fly the airplane. Then, while the engine is still in operating temps, pull the prop through all four compression cycles. Listen for the hiss of air escaping from either the exhaust (valve problem) or the oil filler neck (ring issues). If anything seem amiss, go run the engine some more and try again in case there was a bit of carbon or something blocking a valve temporarily. If you're satisfied with that, remove the oil filter, cut it open, and inspect the material for metal and other particulates. To be pedantic, you can do a differential pressure test, but only if you compare the results to the trends noted in the logbook.
If the engine doesn't pass this inspection, then it is due for repair. A competent mechanic will conduct other diagnosis before cracking it open, such as measuring valve lift if a cam is suspect or borescoping any cylinder suspected of having a bad valve.
O-200s are simple engines and the risks of cracking one open for inspection far outweigh the possible rewards. The only time I've cracked one open for diagnosis was to confirm its crankshaft was broken; something I could already tell through external inspection by the way the rotation of the prop by hand didn't quite sync up with the rotation of the alternator.
As far as logbooks go, take them all with a grain of salt. The standards for recording maintenance entries has changed over the years and not every shop has the same standards. Aircraft operated for commercial purposes will likely have nicer looking logs, but the aircraft itself might have been abused more. I've no problem with damage history, as long as it was repaired correctly. I'd much rather fly an airplane with a rebuilt wing than one that might have corrosion hiding in places unseen since the airplane left the factory fifty years ago.
Cessna 150s are simple, low cost airplanes. Pick one, buy it, fly the heck out of it, and enjoy it. Don't waste time, money, and emotional energy agonizing that you might not pick the best one available. Use your best judgement, then pull the trigger on the purchase.
.
