More details about the alleged illicit business practices of the German art adviser Helge Achenbach have come to light as his trial progresses. Achenbach stands accused of defrauding the late billionaire and Aldi supermarket heir Berthold Albrecht, resulting in estimated damages of €23 million (see Fraud Claim Against Art Adviser).

During the court’s last session, the court heard a testimony from Achenbach’s former associate, art historian Thomas Kellein. He told the court that the adviser had charged pharmaceutical entrepreneur Christian Boehringer “high price premiums,” while Achenbach was managing director of the now-defunct Berenberg Art Advice, a subsidiary of the private Berenberg Bank (see Achenbach Associate Reveals Details of Business Deals).

As the FAZ reports, on Monday Achenbach admitted that he did charge Boehringer hidden premiums. According to his testimony, the business targets set by the art consulting firm were too optimistic, which led him to charge an additional fee on top of the agreed purchase price and commission. “I’m not good at saying no. I try to satisfy all parties. This led me down the wrong path,” Achenbach said, his voice reportedly faltering. It is the second time the art adviser has partially confessed to allegations against him (see Achenbach Gives Surprise Partial-Confession in Fraud Case)

The court also heard testimony from another former Achenbach associate, art historian Stefan Horsthemke, who maintained his own innocence, saying, “At no time did I commit unlawful acts with Mr. Achenbach.” Achenbach later contradicted Horsthemke’s statement, telling the court, “I proposed to share. He didn’t turn it down.”

UPDATE: On Wednesday, Boehringer told the court his version of events. He testified that he negotiated a 5 percent commission with Achenbach. He first became suspicious in the fall of 2012. Boehringer claims that, under pressure, Achenbach showed him a list, which included “additional markups” that were not agreed upon. According to Boehringer, Achenbach apologized and compensated him with €1.1 million ($1.29 million). After the incident Boehringer said it was “inconceivable” for him to work with Achenbach again.