frankleeceo - 4:36 pm on Sep 20, 2013 (gmt 0)
estimated earning is just estimates. They have done end of month processing and take out invalid clicks such as IP or clicks that they deem accidental. That's about all they'll tell you.
We all have amount taken off to some degrees and that number differs from month to month.
Check out the "finalized earning" thread on this subforum and you can get a handle on how you are faring in terms of earning shave.
Most people get shaved within 0~5% range but it can sometimes get to 5~10%, and in some very extreme cases 20~30%.
What % of your total earning is that $300? If it's less than 10% I wouldn't worry, but more than you may have to dig deeper to see where that came from. Consistent high % earning shave may mean that you have a significant portion earned due to invalid clicks for whatever reason, and that is some red flags for both you and Google.