Agree an acceptable cost
For a service business, work back from customer value and the proportion of suitable enquiries that become customers. For a retailer, consider margin, fulfilment, returns and acquisition cost. An awareness campaign has different goals and should be assessed against them.
Keep advertising spend separate from service fees so the cost target is clear.
Review settled results
Use comparable date ranges and allow time for enquiries to be followed up or purchases to be recorded. Check the event being counted, attribution settings and any changes in the offer, stock or tracking.
Look beyond the account
Can the business respond to more enquiries or fulfil more orders? Does the landing page work? Is there enough useful creative to support the campaign? Address the main constraint before increasing spend.
Make a controlled increase
Agree the extra spend, the review point and the result you need. Record other changes to the campaign so the next comparison is useful. There is no single percentage increase that suits every account.
Review the extra outcome
Compare the additional spend with the additional results, alongside the overall trend. Check quality as well as quantity and adjust the plan when costs or capacity change.
Example: £600 in media spend for 20 enquiries is £30 per enquiry. If four become customers, the media cost per customer is £150. These are two different measures of the same activity.
Write down the spending decision
Before changing the budget, record current spend, settled enquiries or purchases, cost per useful outcome, available fulfilment capacity and the extra amount you can afford to test. Set a review date and a stopping condition. In the example above, four customers from 20 enquiries is a 20% observed conversion rate; it is an assumption to revisit when estimating what another £300 might produce, not a guarantee of two more customers.