Bear in mind that there is a vast amount of clicking on "wasted" adverts, i.e. paid adverts which would have been the top result of an organic search anyway, e.g. eBay spending $20M a year on ads targeting the keyword "eBay", which they thought was great because it appeared to give a $245.6m return on investment, until they switched it off for a bit and realised they got pretty much the same traffic and conversion rate without the massive advertising spend[0].
