Be careful buying used equipment. I would never buy a used saw if I either didn't get a guarantee from the seller or if I couldn't at least pull the muffler off and look at the condition of the piston, rings, and cylinder walls.
A farmer that uses his saw to clear fence rows and cuts a lot of dirty wood will likely have bar that looks like crap. But if he does proper maintenance: keeps the air filter clean, uses fresh fuel with the proper mix, etc. should have a decent saw. A weekend warrior that cuts a few cords a year but accidentally ran unmixed fuel through it once, may have the purtiest saw in town, but one that is fully prepped for an early death.
Basically I'm saying that bars, chains, and sprockets are "consumable" items and will not give an accurate representation of the condition of the saw's internals. Cylinders, rings, and pistons are not consumable. Any scoring of the walls and/or piston will cost you lots of $$$ to fix.
God bless,
Chris