Bloodwork is the only way to know for sure.
You want HGH serum level test... Just pin 10iu before test and it'll show if its legit or not.
If your lab doesn't offer that you could try igf1 test but you would need baseline values before hand.
On top of this, it could be real but just handled poorly. For example no refrigeration for long time, shaking the vial when reconstituting etc etc.