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I used to rank 2 for "guitar outlet"  I just dropped to under 50th.  Only change I made was to pause a Adwords campaign where I was including that keyword.  Oddly enough, I believe I ranked high for that keyword BEFORE I added it as a keyword, but I cant be 100% sure due to lack of timing notes.  But is it common for adwords to affect organic?

If not...where do I start to look for the answer as to why it dropped?

You were correct- the KW were listed in my GA.  So, for example, "zt amplifiers"  there have been 3 clicks today, but I am not ranked in google, and I am 80 - 90 rank in yahoo/bing.  So in looking as you suggest at pages and time, I see 100% bounce, 1 page...can I conclude bot?

And if so how do the bots come by way of keywords anyway?  Is that typical?  I always thought they just started at one point and spidered through links as they found them on the page.

I have several keywords that seem to bring visitors in but when I look at my rankings it shows that I have no ranking authority at all.  Are these just robots or some non human click?  Or how do I even get these visitors?