What electronic diagnostics can show
An appropriate tool reads information available from accessible control units. Results depend on the vehicle, system access and reading conditions. Ask which systems were read and which could not be accessed.
A code is not a verdict
A stored code must be considered alongside symptoms and observations. It does not automatically identify a part to replace. Equally, a code-free reading does not validate bodywork, history or every mechanical component.
Define the service you need
For a purchase, clarify whether you need a targeted diagnostic check or a broader assessment with visual checks and, when possible, a road test. Agree scope, exclusions and report arrangements before accepting the price.
This is general reading guidance, not a diagnosis of a particular vehicle. The vehicle and agreed scope determine the service.