What to look for in used baler

It's time to upgrade from my 1952 Oliver 520 baler
I am looking through Craigslist and other places for used balers.
The question is when go to look at a used baler what are the most important items to look at on the baler and what questions do you ask the seller?
Marvin

I would focus on New Holland and John Deere balers. Some of these are getting long in the tooth, so condition/wear becomes more important than age.

Unless it's a project, have the seller hook the baler to a tractor and make a few bales of hay. Look for general signs of abuse, welded needles, newer repaint.

How much do you want to spend, how many bales per year?

Post here about the baler with make/model number if you find something before you buy.

What Bill says, plus look at the knives and plunger rails. Check all of the wear items as it can get real costly to rebuild one.

Check for rust. The only place that is really problematic is at the bale chamber under the knotters. This is where everything mounts. If it is tender in this area whenever you have a heavy charge at the same time as it tries to knot, you will have problems. Another place to check for rust is at the junction of the intake and the chamber right where the knife edge of the plunger head runs.
Check through the drive line from to back. PTO U-joints for slop; Tightness of flywheel on it's shaft; play between input and output of main gearbox, tightness of both ends of plunger head drive rod. With no hay in it: Check chains by seeing how far you can pull the chain from the sprocket. If you can see any tooth tips on the inside of the chain the chain needs replacement. Check sprockets for worn teeth. Leaning over or bent to one side means the sprocket is worn out. Trip the knotters and turn slowly by hand. Watch the needle tips as they get close to the knotters. Advance one inch at a time and watch for variation in distance up and down and side to side from the close parts of both knotters. watch the movement of the bill hook and twine disc for any difference between the two. Check the hay dogs. At this point you are ready to put some hay in loosely and try the knotters. The new old balers will have the pick-up tines only3 inches apart where the older ones will be five inches. This makes a big difference in finer hay. Pretty much everything else is adjustment with the manual once you own it, before trying to use it.

My main concern would be bearings. Before I bought another It'd have a tractor hooked to it and run at PTO speed to check for bad bearings, especially on the main drive rollers. Belts, chains and cylinder packings are easy to replace but changing out a main bearing, working alone as I do, would be a no-no.