Run any machine through ALL its paces before buying it, or you are taking a big chance. You cannot know what might be wrong with a machine without running it. Could have a bad motor, noisy spindle bearings, feeds that don't work, coolant pump not operational, or all of the above and more. Ideally you want to cut metal with it before buying. Anything you cannot make to work properly must be assumed to be nonfunctional.
When I am looking at a machine that cannot be run through its paces, I have to assume the worst case scenario, that nothing works. In that case, for me, it is the same as scrap iron, a collection of parts that only LOOKS like a machine, and scrap iron is worth about $100 a TON. If you have to move it to even find out if it works, you will have much time, effort, and money invested by the time you call the scrapper to come pick it up. That is indeed a negative approach, but people do try to unload their trash on unsuspecting and hopeful, trusting buyers. Private cash sales are always assumed to be without warranty, even if one is offered. Once you transfer the cash to the buyer, it is yours, treasure or trash.
I will tell the seller all of the above and use it for setting a price point if I have any interest at all in the machine. Generally I do not want to even get involved with anything I cannot test drive.
The spindle of a milling machine is easily tested for runout and looseness with an indicator. Runout should be not more than .0005".
