I tinted all my car side windows. Not hard but need experienc

The most difficult one is the back window, because it is curved. I did a hatchback myself, the rest - one I drove without tinting on back until sold, all other back windows were left to pros ($50-70).

You can see the color difference on windows from those two shots:

Before


After


In CA, law requires front two windows not lower than 30%, all other windows have no limitations. Since the law for window tinting is secondary, not enforced (in every state), virtually you can lower it to whatever you want.  I have seen some shops did whatever you asked them to (I am not here encouraging you to go beyond law limits though). I prefer Limo Dark 20% all around.