PoSSeSSeDCoW: I don't think it's despicable at all. They don't seem to have left more than one review and they are, in fact, a user of their product. Is it unethical for their family members, who have played the game, to rate the game as well? How about anyone who knows them? Their 10 score is far more legitimate than morons like ChickenHero who will rate a product a 0 to "punish" the companies and haven't played the games. It's far more despicable when people who haven't played a game rate a game a zero because of some perceived slight against them, be it DRM, cosmetic DLC, or the game is just "too" popular.
These people get touted on gog as if they're doing something constructive, when in reality they're showing how many childish gamers are.
It is despicable, not that they would reviwew a product in which they have a stake in, but that they do it without properly disclosing their stake. Their actions do nothing but contribute to the general permissiveness and promiscuity regarding the fudgery bewteen roles/entities that flood society at large, and while here we are talking about nickle and dime implications i'm sure i don't have to tell you about the reach of the implications of the same non-disclosure principle taken to other areas of our lives.
In regards to stances like the one outlined by ChickenHero, from where i stand it's basically joining these 'legitimate reviwers of their own products' in their own cesspool. Some will undoubetly do it because they preceive it as the only way they have to counterbalance the industry's institutionalized cheating. Still, nothing to toot about or be proud of.
Edit: Typo's.