There seems to be somewhat of a consensus in the industry that The person who mixes a project should not be the one to master it. Someone earlier mentioned having an editor read your manuscipt, and that is an appropriate analogy. A fresh, unbiased pair of ears is likely to catch things that you are missing.

Of course, it all depends on what you are trying to accomplish. But if you are preparing a project for release, or for pitching to labels, I would recommend that you hire an experienced mastering studio for the job. It's really not that expensive.

Good luck.