Complex issues requiring deeper investigation: corrupted installs, database problems, multi-plugin conflicts, broken migrations. When the root cause isn't obvious and the fix requires significant technical work.
Standard fixes cover issues that involve multiple interacting components, require database-level work, or take significant time to isolate and resolve. These are the cases where random plugin disabling won't work — you need methodical investigation.
I access the site at the server level — SSH, database, and file system. I work from the bottom up: server environment first, then PHP configuration, then WordPress core, then plugins and theme. Every step is documented and reversible.
Backup first, always: Before any fix work begins, I verify a backup exists. If not, I create one. No exceptions.