Why have your mastering done by someone else?
1. No matter how good a mixing engineer's work might be, nobody can change the fact that although the skills of mixing and mastering are related, they are also very different.What's more, the person who just mixed your music simply cannot hear it with the fresh pair of ears that is needed to get the best possible result out of the mastering process.
2. The majority of recording/mixing studios do not have the necessary equipment to do a quality mastering job. A wavelab may well make your music loud, but that alone will by no means make it sound the best that it can!
Why not have a trial master done and judge for yourself?