I bought used, sight unseen, but I did get hold of an independant Haas tech (who lived in the locality of the machine for sale) to look at the machine on my behalf. I also had him perform a memory upgrade for me, which required some board changes and newer software. I spent about $5000 extra at that time, and that included some new way covers.
The results: acceptable, IMO. I ran the machine as I received it for a year or so, then replaced the spindle bearings because I thought it was getting noisy.
I think if the tech pulls back the way covers, and finds whether the ways are getting oiled properly, that is probably your main concern. If the orifices are functional, it is a good indication that the linear ways are most likely in good to excellent condition.
A backlash examination would be easy enough to do. The tech can do this, perhaps even run a ballbar test on the machine for you. A good machine will have minimal settings in the backlash compensation registers. Extreme backlash indicates probably bad thrust bearings, and I can't imagine that this is a major hurdle to fix. Bad ballscrews would be much more expensive, but if the lube system is working, the ballscrews will last a long time, and will most likely be quite noisy in operation if they are at all bad.
Pulling back the way covers means that you can also find the real story on what the machine was cutting. If you were to find abrasives in there, run
1996 and newer had brushless servos, which is a plus IMO, because one less thing to fuss with (bad brushes). They also are capable of the 710 ipm rapid.
First you get good, then you get fast. Then grouchiness sets in.
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)