(Bloomberg) — Apple Inc.’s attempts to justify the 27% fee it charges developers for purchases outside its App Store backfired as a skeptical federal judge questioned an executive about a company-commissioned study showing half that rate would be reasonable.

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US District Judge Yvonne Gonzalez Rogers in Oakland, California, heard a fourth day of testimony to determine whether the iPhone maker is abiding by a 2021 court order in an antitrust case brought by Fortnite-maker Epic Games Inc., which included allowing app developers to link to payment options not controlled by Apple.

Carson Oliver, senior director for business management for the App Store, testified Friday that Apple hired economic consulting firm Analysis Group Inc. to help create a new commission rate for purchases.

But Rogers repeatedly chastised Oliver for statements about how Apple decided it would charge developers 27% for purchases of digital goods or services made outside its App Store, given that the lowest end of the range in the Analysis Group study is 12.3%.

“How did you justify the other 15% you are charging?” she said.

Apple provides a number of services to developers including discovery of apps, distribution, developer tools and platform technology, along with additional privacy, user trust and safety that aren’t comparable to other platforms, Oliver testified. He said Apple estimates the true low-end was 17%.

Analysis Group estimated what each of those categories was worth by comparing them to what is charged by platforms including Microsoft Corp., Alphabet Inc.’s Google, Etsy Inc. and Shopify Inc.

The Analysis Group study found the value of those services would amount to between 12.3% at the low end or 92% at the high end depending on factors like the size of the developer, Oliver said.

“And you are charging 27%,” Rogers interjected.

Oliver said Apple executives believe the effective rate of the commission is lower than that.

“That’s a big assumption,” the judge replied. “Your assumptions are just that — they are assumptions. There’s no data for it.”

“That’s not true,” Oliver said.

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