Amazon has been the cornerstone of convenience, with shoppers able to make purchases in the spur of the moment.

But some customers are buying food from third-party companies, about 2.5 million of them, that use Amazon's Marketplace to sell and fulfill orders, and some of those companies are leaving customers upset with the online retailer, CNBC reported.

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Customers are saying they've been sent expired foods including baby formula, coffee creamer and granola bars, CNBC reported.

Some of the food wasn't just outdated but outright spoiled, according to shoppers.

Some customers who purchased a 2-pound bag of Teavana Beach Bellini last year said it had a strong chemical smell. One person equated it to the smell of nail polish remover, while others said it must have gone bad. Starbucks closed the Teavana chain in 2017, CNBC reported.

There are some reviews that said purchases of the same items were just as expected and tasted fine.

The tea is still for sale on Amazon.

One woman alerted Amazon when she received brownies that had expired in 2018, but were shipped in 2019. She realized they were outdated after eating one. Amazon did eventually give her a refund.

Amazon told CNBC it has tools to combat the selling of outdated food. Items must be within the boundaries of Amazon's policies and must have at least 90 days remaining on the item's shelf life.

Anything within 50 days of expiring when it arrives at Amazon warehouses will be marked for disposal by Amazon employees, according to Seller Central on the Amazon website.

Amazon said the expired food issues were isolated instances, and that the issues didn't require enforcement against sellers or the removal of items, CNBC reported.

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