The company gives guidance, so the estimates are not pulled out of thin air. Google should know their ad business very well at this point.
People selling after an ad miss is medium/long term thinking. They could be wrong, but was the miss caused by a wider economic slowdown (see UPS earnings) or was it Google specific? Either way, it could be sign of Google slowing down or the economy as whole.
That's not true, and hasn't been for a decade. For this earnings release, the proportion of revenue from ads was 76%.
> The company gives guidance
No, they don't. As far as I know they've literally never given guidance.
If you truly believe Google releases guidance, how about you just find a quote for what that supposed guidance was for Q4? You won't find it, because Google does not release guidance. The GP just made it up, just like they made up the numbers.
Also, if you only consider the search revenue you'll err in the opposite direction. It's 55% of their revenue, so pretty soon not even a normal majority. You should look at the "Google Advertising" line.