Well if you keep tabs on what you are doing and taking in, like everything being equal, and the only additive is the GH compared to previous conditions, it's a safe bet that any improvments is contributed to that one added compound. Now i don't assume i know it all, but what i have learned and do know is mainly based on my experience. I have tried things that might go against the grain concerning bodybuiliding, but the outcome more than not has been pleasing. As for placebo affect being a powerful thing for some, i try to keep an open mind and not focus on the compound being used.
As an example, in 03 my first experience whith G(serostim). It was taken before bed(2iu i believe) the first week. I would wake up in the middle of the night with excruciating pain in my elbow(tendinitis). By the second week while training tris. it all of a sudden hit me, the pain in my elbow was gone. I only took it for 8 weeks til i ran out, but it seem like after the first few weeks i wasn't "feeling" much anymore. Nothing comes close to my first course of serostim.
I also agree that most coming from china is garbage