tedster - 5:15 pm on Sep 16, 2010 (gmt 0) [edited by: tedster at 9:32 pm (utc) on Sep 16, 2010]
If you're going to be proactive, then you're first going to need an accurate diagnosis - the root cause. Your sales changes may not even reflect a change in the Google SERPs, you know? And since this thread discusses SERP changes, it's hard for anyone to offer you any insights if you only know the sales changes and not the ranking changes.
[edited by: tedster at 9:32 pm (utc) on Sep 16, 2010]