I have read that if you buy a used, maxed out H9 Core, it will always be Maxed out.  Just wanted to make sure one last time.  Also, what is the best way to see if the unit is Maxed out when I go check it out? 

If an H9 is maxed out, it becomes and will always be a Max.

Please take a look at this page, which tells you how to check the MaxOut progress. You may also go to Settings->Eventide Account in H9 Control, to find out what is the type of your H9.