When reviewing you must have knowledge about the product. If you don't then you won't be able to leave an accurate review.
No matter what you say about a product that's not going to affect the cost or the availability. But it will affect the image or in other words affect what people think about the product.
And fair. You must be fair about your review. Even if you don't like the company doesn't mean that the product is bad. You must be fair and give factual information.
