Yes, we have different confidence slices: if person clicked on banner, and made purchase in YY mins, it is XX% probability that banner was main deciding factor.

Yes, we have different confidence slices: if person clicked on banner, and made purchase in YY mins, it is XX% probability that banner was main deciding factor. Now, you run trial campaigns for your product, collect data, and calculate XX base on it, and transfer this XX into your bidding formula. Or trust Google/FB/etc bidding algorithms/ML to do this for you.