If you want a writer following your "rules" then you need to train them. I actually don't look at what my writer writes anymore and he is the one publishing it. I know that he is writing good stuff as I've trained him properly.
How you do the training varies from what you want. Maybe give a clear template of the review?
Here is an example:
Write a introduction, pros, cons, features and conclusion about the product. I want you to talk in first-person perspective so that it sounds that you frequently use this product or like you are a satisfied consumer. I want you to not mention prize nor the rating it got on Amazon at it could lead to me getting banned - also, here is a good example article so that you can see what I look for: *LINK*.
- End of example -
It all comes down to doing proper training so that they do like you want them to, it is impossible for them to know that without any training.
I made a guide about how I found my writer that I now have hired full-time:
http://www.blackhatworld.com/blackh...85592-guide-how-i-find-writers-0-6-100-a.html. A lot of people have used the same approach and have gotten even cheaper rates!
Good luck!