We get one version of this call every few months: a founder has inherited a codebase from a previous developer or agency, it is slow or unstable, and they want to know whether to fix it or start over. The honest answer requires an audit, and skipping that step is the single most expensive mistake we see clients make.
What an audit actually checks
A proper technical audit covers the data model, the authentication and authorization approach, dependency versions and known vulnerabilities, test coverage if any exists, and how the application behaves under realistic load. Most of that is invisible from the outside, which is exactly why it gets skipped.
Rebuilding without an audit repeats the same mistakes
We have seen full rebuilds recreate the exact bug that motivated the rebuild in the first place, because nobody diagnosed the root cause before writing new code. A rebuild without an audit is a guess wearing a fresh coat of paint.
Sometimes the answer is not to rebuild
An audit occasionally concludes that the existing system is salvageable with targeted fixes, at a fraction of a full rebuild's cost. We would rather tell a prospective client that than sell a rebuild they do not need.