Start with the review
Before building an automated process, decide what someone will need to check. Identify the source population, expected control totals, key assumptions and the exceptions that require attention. Those requirements influence the data model and the output.
Keep the path to the source
A useful result retains references to the underlying transactions or records. A reviewer should be able to trace a value back to the source and understand how transformations, mappings and exclusions affected it.
Make exceptions visible
A failed import, unmapped entity or unexpected currency should produce a visible exception. Quietly omitting records can leave an apparently plausible answer that is incomplete. Design the response to exceptions with the people who will operate the process.
Support the next person
Document the purpose, inputs, dependencies and recovery steps. The solution should be understandable to the team responsible for supporting it after the initial build.