Three things need to be true before spending is a good idea, and they are testable rather than a matter of judgment. You know what a customer is worth to you in gross profit, not revenue. Something already converts, meaning people who arrive through referral or search actually contact you at some rate you can name. And conversion tracking is installed and verified, so you will be able to tell what the money did. A study of five hundred small business advertising accounts found fewer than half had conversion tracking in place, which means most of that spending was unmeasurable from the first day.
If those hold, size the first budget as a learning cost rather than a growth investment. You are buying the answer to a question, which is whether you can acquire a customer profitably through this channel, and the budget needs to be large enough to reach a conclusion. Work backward: if a customer is worth two hundred dollars in gross profit and you expect to convert somewhere around one in twenty inquiries, you need enough clicks to produce a meaningful number of inquiries before the data means anything. In most local service categories that is several hundred dollars a month for at least two or three months, not fifty dollars for a week.
Set the stopping rule before you start, because deciding afterward is how both common errors happen. People quit at three weeks when the campaign needed eight, or they continue for a year because stopping would mean admitting the spending was wasted. Write down what result would justify continuing, what result would mean stopping, and the date you will decide. Then hold to it.
Spend it on the narrowest, highest intent thing available rather than the broadest. Somebody searching for exactly what you sell in the city where you operate is worth many times somebody who matched a demographic profile. Start with search intent in your service area, keep the keyword list tight, add negative keywords aggressively, and send the traffic to a page built for that specific query rather than to your home page. Roughly a quarter of small business advertising budgets are estimated to be wasted through structural and management errors rather than through the channel itself, and most of that waste is broad targeting pointed at a general page.