How does the rep work

[Weather]

How does the rep work  since some contracts say stars 7(-3)

[Streetwind]

7 is the actual value you will get getting. The -3 tells you that this used to be 10, but something is modifying the contract to pay out less reputation. Could be a strategy activated in the admin building that does this, for example.

Your reputation is simply a number that adds up. In your case it will increase by 7 when you complete this contract. You cannot directly see the the sum total you have easily, but the higher the number is, the greener your reputation indicator in the middle of the top bar in the space center view becomes.

Reputation has diminishing returns. The sum total always increases linearly, but you get less and less from the same increase the more you already have.

That doesn't really matter though, because reputation has close to no discernible effect on your game as long as it isn't negative.