In July 2019, EU regulators accused the online retailer of manipulating its algorithm to boost its own products "artificially" over its rivals. As a result, they alleged, users often end up buying lower-quality products at a higher price.

But according to the Financial Times, EU officials are struggling to understand how Amazon's algorithm works, despite sending a series of detailed questions to the company about the criteria used to boost a product's visibility.

These people added that officials are also unlikely to be able to view the online retailer's proprietary code directly to build their case, owing to legal barriers around trade secrets. Antitrust investigators frequently face hurdles in navigating the "black boxes" of technology companies' code.

"Cases involving algorithms are complex", said a Brussels-based legal expert. "But the EU doesn't have to dictate how a computer code works. It is for the company that uses the algorithm to deliver a fair result." However multiple people noted that the EU's case against Amazon is proceeding more slowly than other comparable investigations. The bloc is already set to bring charges against Apple over alleged abuse of its dominant platform in music streaming, for instance, after a two year long probe.