Improve error messages in models

**Problem**
When working with services, the error messages could be more descriptive.

**Suggestion**
Improve error handling and add detailed error messages.

**Context**
This would help with debugging and maintenance.

No files, tests, or entry points are identified. First locate the service and model error-handling paths, then determine which failures need more descriptive messages; done means the relevant errors provide detailed debugging context and the existing checks still pass.

Written by the indexing model from the issue text.