You could fill a lifetime with the answers to your questions...but....
www.mermac.com has some pointers for inspecting used machinery.
"Good used American" is generally a safe bet. The trick, of course, is the "good" part. Worn out, the finest machine is a boat anchor. Clausing, South Bend, Logan, all made good stuff. Emco, made in Austria (NOT! ENCO!!!) is also excellent quality, if you find any, although parts may be hard to come by.
Try to make a living, not a killing. -- Utah Phillips
Don't believe everything you know. -- Bumper sticker
Everybody is ignorant, only on different subjects. -- Will Rogers
There are lots of people who mistake their imagination for their memory. - Josh Billings
Law of Logical Argument - Anything is possible if you don't know what you are talking about.