Final answer:
The correct statement is that Kopel should have requested underlying documentation before deducting the $3,000 to verify the accuracy of Raff's tax information and adhere to professional tax preparation standards.
Step-by-step explanation:
The correct statement is that Kopel should have requested underlying documentation before deducting the $3,000. As a tax preparer, it is Kopel's professional responsibility to exercise due diligence in preparing taxpayers' returns. This includes verifying the accuracy of the information provided by the taxpayer.
Even though Kopel may not be held responsible for the understatement of Raff's tax liability since he had no reason to believe the information was incorrect, it is best practice to request documentation for significant deductions to ensure the accuracy of the return. Therefore, Kopel doing so could prevent any potential issues with incorrect reporting, which can lead to penalties and interest charges if an audit were to occur.