Amazon is a gigantic international marketplace filled with all sorts of goods from countless manufacturers and vendors—a selection so broad, it can easily overwhelm shoppers. Though the company doesn't really curate what's sold on its platform, it does do the equivalent of showing off certain products in the window with its "Amazon's Choice" label. The problem is that nobody outside Amazon knows how those choices get chosen... and some of those "choice" products are basically crap.

Several media outlets have tried and failed to learn how it all works, but this week members of the Senate have come knocking on Amazon's metaphorical door with some pointed questions. Democrats Bob Menendez of New Jersey and Richard Blumenthal of Connecticut are calling on Amazon to explain why certain products get that coveted Amazon's Choice badge to determine if the moniker "deceives consumers into purchasing products of inferior quality."

A search for a product like dish detergent returns more than 20,000 results, Blumenthal and Menendez write in a letter (PDF) addressed to Amazon CEO Jeff Bezos. Given that volume, consumers "look for distinctive product features to help narrow the extensive search results," and those shoppers "reasonably rely" on the Amazon's Choice label "to guide their final purchasing decisions."

The label does indeed seem to guide purchasing decisions, the senators note in their press release. A research study showed that products granted Amazon's Choice status can see a threefold sales increase—but products that have the badge and then lose it see sales slump by 30%.

Amazon introduced the "Choice" feature in 2015 as a way to create a default for shoppers talking to their Alexa-enabled devices to buy goods. "Alexa, buy dish soap" is one thing if you buy the same kind of dish soap every month, but what if you have no purchase history? You can't easily browse 20,000 items—or even 20 items—when you're talking to a speaker. So Amazon's Choice product became what Alexa would suggest for you up front.

These "choice" products can be of dubious quality, as highlighted by a BuzzFeed News report from June. BuzzFeed found dozens of instances of consumers complaining, both in Amazon reviews and elsewhere on social media, about Amazon's Choice products that broke down or just plain didn't work—including a thermometer where the product description itself said the item was "widely inaccurate."

"I took the Amazon's Choice label as an endorsement by Amazon, although I later found out that's more of an algorithmic term," one Amazon shopper told BuzzFeed at the time. "I find that to be confusing at best, misleading at worst."

Pay to place?

The letter gives Amazon until September 16 to respond to a whole host of questions about how the Amazon's Choice label gets assigned, starting with a request for a detailed description of the process and whether it's purely algorithmic or if human hands are ever involved. It also asks if all Amazon shoppers see the same "choice" products or if the label varies between shoppers based on individual purchase and browsing histories.

The senators also want to know what metrics Amazon uses to make the call. As part of that, the letter also asks Amazon to define what "highly rated" means, in context, especially given the challenges the company has faced in the past with fraudulent, paid-for reviews and review recycling, in which a lesser product is swapped into the listing of a different product that already has a positive rating.

The Amazon's Choice moniker may mean Amazon is "actively promoting products with fraudulent reviews" and exacerbating the problem, the senators write. The company may also be unfairly disadvantaging competitors in the marketplace by promoting its own private-label brands (which are not always marked as Amazon brands) over others.

"Amazon bears the responsibility of providing its customers with accurate information" so shoppers can make informed decisions, the senators write. "Unfortunately, Amazon has failed to fulfill this responsibility."