Basic gig includes bug fixing in your game script or platform related issues. This includes build issues (Windows/Android)
Standard gig includes new game mechanic/feature to your game. This can be Google Play service, Login/Register function.
Premium gig includes guidance, how-to and commented section for you to better understanding game logic or more complex game mechanic like multiplayer game.
If you have any question about Unity game development, don't hesitate to message.