You don't have to be a professional, because you're an amateur. That being said, you should still give off an air of professionalism and class. Knowing a lot about your product/hobby is nice too, but not an absolute must as consumers are not always savvy enough to differentiate a true expert from someone with good video editing skills. Read up as much as you can, (all the headroom guides, the head-fi stickies, headwize articles etc.,) and get some experience with various models so that you have a baseline to compare to. 8.3 may seem reasonable to you now, but to people with more experience the vaunted HD800 (Sennheiser's current top model with a $1500 price tag) only has a weighted average of
7.9/10.*
That being said, you don't have to cater to the audiophile community. You can review for a demographic of "normal" people who are just looking for something with decent build and sound quality without paying a premium. There's a market for that. But like any market you need marketability. Better video quality, rehearse what you're going to say beforehand, get someone with editing skills to help you out if need be. Get someone to edit your reviews/articles. Have headings, maybe with simple bullet points if you're not going to get too specific. Your paragraphs are too long and many sentences are non-sequiturs.
These are a couple ideas just to give you an idea of the minimum that it would take for companies to want to send you their gear for reviews, and even then it's their prerogative and there is no guarantee.
*Anyone have any idea what happened to this site? It used to be really active, I actually used it for a couple years before I ever found Head-Fi. I actually knew I wanted a Stax setup before I even joined Head-Fi thanks to these guys...