Unless you want a project on your hands, just walk away if you see any signs of abuse or neglect. Things like rust, damaged parts (other than minor shell dings), missing parts, peeling wrap, etc. If the heads are worn, that’s likely fine since they’re easily replaceable. But if they look beat to within an inch of their life, then I’d definitely take off the head(s) and inspect the bearing edges to make sure those aren’t beat to hell as well.
Other than that, if they appear to be in good condition, they most likely are.