The case referred to is U.S. v. Stinson, a federal appeals decision that affirmed the disgorgement (repayment) of $949,952.47 against a tax return preparer. Disgorgement, which compels wrongdoers to repay the gains of illegal business activity, is a civil "remedy" arising from equitable principles. It aims to prevent or deter unjust enrichment, a scenario where one person becomes enriched at the expense of another. Disgorgement is often pursued by the Securities & Exchange Commission. A five year statute of limitations applies.
In the world of taxation, Stinson reflects a growing trend by the government to seek disgorgement from tax-return preparers in "civil injunction" cases.
Similar to criminal cases, the amount of restitution in civil tax cases need not be precisely determined. The court is expected to make only "reasonable extrapolations from known samples." Just a "reasonable estimate" is required.
A helpful summary of Stinson can be found here.