I think it's merch food.
A max staff has a base of ...
20% HSR all spells
+10 energy
11-22 damage (if you meet the listed requirement)
An inscribable staff has an inscription slot "Inscription: ..."
Non-inscribable staffs can have one more inherent modifier like:
- reduces some condition
- up to 10% HCT all spells
- up to 20% HCT a specific attribute's spells (not necessarily the same attribute as your staff's requirement)
Staffs with max base but no inscription slot or desirable inherent mod are usually merch food unless they are an especially rare/desired skin (in which case, such limited functionality versions might fetch a few plat.)
You say it's not inscribable, but you don't list anything that looks like a built in "inherent bonus." Shadow Staffs don't seem to be a particularly rare or valuable skin as staffs go. So that's why I think yours is merch food. Sorry