What is a two-click flow in search arbitrage?
A two-click flow means the visitor clicks twice before the publisher earns anything. The first click is on a suggested search term on the landing page. The second is on a sponsored result on the search page that follows. Only the second click is paid. The extra step filters out visitors who are not really interested.
The two-click flow exists to protect advertisers. A person who picks a term and then picks an ad has shown search intent twice, so the click is more likely to be worth what the advertiser bid. A one-click flow, where the first click from the lander already lands on an advertiser, converts worse and has mostly been pushed out of Google's programmes.
The cost is drop-off. As an illustration, if 45% of visitors click a term and 40% of those click an ad, only 18% of visitors produce a monetised click. Each of those clicks has to earn enough to pay for the other 82%.