Already for a long time there is a system of payment on the fact, that is advertising is paid for each given client. this has been present for a long time and quite successfully.
The final meaning it does not change. There is an amount of work (advertising) there is a conversion (customers) if the ratio does not satisfy the demands of the advertising company then it simply will not do this work.
In the example that you bring the conversion depends on the product. So it must be excellent.