Some of the mastering engineers on discuss their approaches to mastering:

One reason to use EQ post compression is so that you don’t have to keep re-adjusting the threshold of the compressor when making EQ changes.

This insightful thread on ProSound addresses the consequences of mixing and mastering in the same room:

Bob Ludwig always used to warn people not to listen back to mastered material in the mixing environment, because any room anomolies (which already would have affected your mixes in the first instance) would be now doubly magnified by the “re-playing” through the same system.

This advice would apply in spades to a non-professionally treated room.

Finally, though it ends well, this tale from illustrates why we should be wary of budget mastering offers in the Internet:

I definitely feel robbed. Great!

I suppose use me as a reminder to enquire first and to avoid this online mastering company. I most certainly fell for it. A $60 lesson.