Good Morning Skip,
There are a couple of quick ways to determine if the machine has seen a lot of wear. take a flashlight and crank the saddle to the right. Look at the rack under the way and see if the rack teeth all look the same. The left and right end of the rack will be like new, but about a foot to the right of the head stock (HS), that where the wear generally is. Look at the bed-ways near the HS and see if there are any dents in the ways, look at the top of the front male V way and see if there is a ridge that our fingernail will catch on, this is wear. crank the saddle in and look for scratches and dirt, if the way surfaces are dirty and scratched, the former owner did not clean and oil it properly. Crank out the Tail Stock (TS) quill and look at it for scratches wrap you hand around it and see if it will turn or there is a lot of play, if it does the key is worn. Look inside the TS taper and see it is all dinged up or smooth. If you really want to take some time and if the owner will let you take the HS top cover off and look at the gears, see if he has tightened the spindle bearings, look at the drive V belts and see if they are worn.
See if he has an air hose hanging on the machine, see if he has a oil can with way oil near it. See if he has wiped off the machine, does he have a manual? Just do some common sense tests and run it, ask if he has ever had to repair anything. I get a kick out of someone who goes and looks at a machine and never runs it. He trusts the seller that it run OK. I always say when you go look at a used car do you start it? Do you take it for a test drive? The same applies to checking a machine. I hope the info helps you and other potential buyers. Rich