Only one review per user

Hello,

I have frontend user posting, and i am having 2 problems:

1. The user that posted a product can give his own product a review with star (multiple time) and this make the rating biased.

2. A user can give the same product multiple review.

What i want is that:

1. The author of a product should not be able to give a review on this product

2. A user can review a product only one time

Kindly advice how to do that?