Well, Bring a stock of Aluminum/ steel with you the next time when you are going to see the machine and ask one of their operator cut you a part that you ask for........ a straight cut with a nice sphere and ID blah blah...... measure the part. Then you can tell 60% about the machine performance, but don't tell them you will do that when you come, cause they can cheat or twist like prepare ahead of time.......... this way if machine have some flauds you can see. It's still not a proof but at least you can eliminate some worry. Shut the machine off for few minutes and then turn it back on see the machine still able to read all the parameters, otherwise the machine this old it's a **tch to find the all right parameters for it. And to check Turret alignment respect spindle slap on the indicator, you can predit how bad the crack was.
Regardless how careful you are something you will find out about the machine that will not work perfect, the machine had been with them so long they know what wrong so they can just smooth that pot out. But if you find some thing right there then you can work out the better deal with them.
My 2 cent.
The best way to learn is trial error.