When you talk to Google sales they want to know how much you make per customer, so theyre able to figure out exactly how much they could charge to take 80% of the margin. The cream on top is taken by Google in the form of fake bot clicks.
IF you have things right - which Google has incentive to see to it that you don't - this makes no difference. Because the real measure isn't how much you make per customer, (including those who come by other means) - it people who didn't click on the ad even though seeing it was a part of their decision to buy (they saw the ad on their phone and told their wife who bought it). If you are doing proper add effectiveness measurement you get this data (it is messy data).
Remember what matters is how the ad affects the bottom line. Everything else is just a proxy - you need to check to see if your proxies are good enough.
