How do you prioritise budgets when the margin is thin?

On a thin margin you advertise only the search where someone already wants to book or ask for an appointment in your area, and you switch the rest off. The little money is not split across display, video and brand. Work out how many low-margin tables or appointments fit in the week's cap. If not even one fits, there is no ad that week. Three campaigns are switched on “to test” and each eats a third without reaching one booking. The month ends with nobody knowing which failed. One campaign, one radius and a written cap. After fifteen days, either there are contacts that cover that cap or it is paused.