Riddle Aggregates (Tax Court rebuttal expert)

What happened

Riddle Aggregates is a conservation easement valuation case tried in the United States Tax Court at Atlanta. The Commissioner of Internal Revenue retained a rebuttal appraisal expert, identified in the transcript as Mr. Sellers, and offered two rebuttal reports as Exhibits 9006-R and 9007-R.

On voir dire, the expert testified that he regularly uses Grammarly and has used ChatGPT and Gemini. The petitioner's examination established that the two rebuttal reports contained citations to sections of the Yellow Book that do not exist, together with other authority that could not be located. Some of these had been corrected by errata sheet. Others surfaced for the first time in the courtroom.

This is a pattern worth naming precisely. The expert whose work failed here was the government's, and the failure was exposed not by a post-trial motion but by questioning in front of the judge.

What the court did

The petitioner objected under Tax Court Rule 143(g)(2) and moved to exclude both exhibits. Judge Kerrigan did not exclude them. She observed that the rule's "language is really [not] fitted to this situation," and then said: "I have grave concerns about this report and in my opinion I probably will address my ... grave concerns about it," and "I'm not clear exactly from the witness' answers what he used to write this."

She ruled that there would be no additional direct examination of the witness. She told the Commissioner's counsel that if the Commissioner stood on the reports as direct testimony, "the Court will admit it," but with concerns "about the reliability."

After a recess, counsel for the Commissioner stated: "Respondent believes the best path forward is going to be to withdraw Exhibits 9006-R and 9007-R in light of the Court's comments." The witness was excused. The case proceeded with a different rebuttal expert.

Where it stands

The reports were withdrawn on March 18, 2026. There is no written order on the artificial intelligence question, and none was located as of September 17, 2026. The record of what happened is the trial transcript.

Judge Kerrigan referred on the record to an October 2024 order by Judge Buch in Tax Court Docket No. 10795-22 addressing artificial intelligence. That order was not obtained.

The obligation it engaged

The conduct engaged Clause 3 of the Standard, independent authority. A citation to a Yellow Book section is a representation that the section exists and says what the report attributes to it. In an appraisal rebuttal, those citations are the standard against which the opposing appraiser's work is being measured, so a fabricated one does not merely decorate the opinion, it supplies the yardstick.

Clause 7, contemporaneous record, is what Judge Kerrigan was reaching for when she said she was not clear what the witness used to write the report. The question came at trial, under oath, with no notice. An expert who keeps a record as the work proceeds can answer it in a sentence. An expert who does not is left describing his habits, and the answer sounded like habits.

There is a separate lesson for retaining counsel. The errata sheet corrected some of the citations before trial, which means somebody found them. Finding some and not all is worse than finding none, because it establishes that the report was checkable and was not fully checked.

Sources

• United States Tax Court · March 18, 2026
  Trial Transcript Volume 3, Riddle Aggregates, LLC v. Commissioner, No. 31104-21
• Damien Charlotin · September 17, 2026
  AI Hallucination Cases database

What could not be confirmed

The primary record is a trial transcript, not an order. The expert is identified in the transcript by surname only. No written opinion or order addressing the artificial intelligence question was located. The October 2024 order of Judge Buch in Tax Court Docket No. 10795-22, referenced on the record, was not obtained. Whether the Court addressed its stated concerns in a later opinion is unknown.