Preventing fraud before it happens
Most small business fraud is internal, undramatic, and runs for years before anyone notices.
Separation of duties, even at small size
The person writing checks isn't the person reconciling the account. The person taking payments isn't the only one seeing the deposit. Layer the controls.
Owner reviews bank statements monthly
Not the bookkeeper's summary, the actual statement. Five minutes a month catches things software misses.
Annual outside review
Once a year, an accountant who isn't the bookkeeper looks at the books. Modest cost, high deterrence value.
Take your version of this question further
This is one operator-tested angle on the question. Your shop, your size, your trade, and your team change the answer. Ask your specific version inside Ask a Shop Owner to get a response grounded in how owners like you actually handled it.