Desktop appraisal is complicated and any halfway decent explanation would be beyond longwinded...especially with a midrange specimen like this one. Without firsthand inspection and knowing your way around one of these machines, it's a gamble. The short version, $1500 isn't too far above the low range for a decent-running machine of this era that is straight & complete. Z50 values are generally lower than CT70s however, the difference is close to the cost spread of restoring them. AFAICT, this one seems a reasonable gamble...for the money being asked...and for the reasons already stated.
Assuming that you just want a decent, reliable, rider for the youngster(s), this may be a good choice. I would throw a new set of tires, tubes & brakes at it. Those are safety items that don't age well. Whilst you're taking care of those items, you'll have an easy time inspecting the cables & controls, as well as the wheel bearings.
