never "mastered" my own work. i don't have the tools that a mastering house uses to do the job so i find it counterproductive to do work on something that I am not equipped to handle. i mean, you don't fix a car if you've got the tools that a baker uses for his trade; apples and oranges, you know?
how would i judge that a work is suitable for mastering? if it is a full fledged project. if its a demo, i don't even bother.