One way to protect yourself is to have an expert look at a used machine.
A machinery repairman may charge $75 an hour to look at a machine. You know what you are getting, and any repairs needed can be haggled over. Before the sale.
Machine repair is expensive. Rebuilding a compound on a Hardinge 59 was $2500.......30 years ago.
Bearings in the headstock of a 13x30 lathe can cost $3500.......plus installation. That was 20 years ago.
Just be careful of bargains.
Another way is to get a cheap lathe, run it and findout what you REALLY want/need in a lathe. Keesp the first one for polishing and such.