With my past experiences in Mastering studios, I had the possibilities to learn how to master a song properly according to the various format available nowadays.
I can then master your song, but I will always advise to have it mastered by someone else if I am mixing your song. I can link you to some of my favorite mastering engineers (amazing sound and very reasonable prices).
Hurt The Fly
Here is an example of a before/after mastering comparison. Mastering is not about changing the whole mix but rather enhancing it and making it fits to every listening environment. It is a subtle but necessary step to take before releasing a song to the world.