ideally you'd want as much expertise as you can afford on this stage of your production, and that's the reason why mastering is rather pricey. it's not just about processing your audio, and getting them as loud as possible, it's also about being aware of the quirks of the target media, and being aware of the methods by which your audio is going to sound over duplicated CDs, the radio, on the TV, etc.
hope this helps.