Not being a dob expert I would just guess like with other scopes-
1/ mirrors clean reflective?
2/ collimation knobs work can turn and can move mirrors-ie not jammed
3/ mount if wood not rotten or showing moisture damage
4/ lens if offered clean
5/ focuser smooth not loose holds eye pieces appears square/aligned
6/ easy to balance with EPS in
7/ clean undented OTA
8/ movements are smooth and not requiring excess force
right price!
Graz
