A new investigation from CNBC revealed that Amazon's third-party sellers are shipping expired food items to customers.

CNBC scoured Amazon's site and found numerous examples of products such as Doritos, beef jerky, and baby food, which had complaints from customers about the items they received being stale or out-of-date.

A spokesperson for Amazon told Business Insider that it has "proactive processes in place to ensure customers receive products with sufficient shelf life." It's unclear how effective Amazon is at policing these rules.

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Amazon's sprawling and increasingly controversial third-party marketplace became the subject of a fresh investigation on Sunday.

This time it came from CNBC, which shed light on dozens of reviews from angry customers who say they were sent expired food after ordering from third-party sellers on Amazon's site.

CNBC scoured the site to find numerous examples of products such as Doritos, beef jerky, and baby food, which had complaints from customers about the item being stale, moldy, or out-of-date. In some cases, customers found that items had expired as much as a year before.

In one review of Half & Half creamers from 2017, a customer said that while the product was in date, it was due to expire within the next 47 days and given that there were 360 creamers, this seemed like an impossible task.

"I can't possibly use 360 in that period of time. This box had a red label hiding the expiration date and there was a line drawn by a marker pen under the label. I have bought boxes of the Carnation Half & Half from Amazon many times that were not close to expiring. Usually I have almost 3 months to use them," the angry customer wrote.

In a statement emailed to Business Insider, a spokesperson for Amazon said it has "proactive processes in place to ensure customers receive products with sufficient shelf life"; these processes are listed online but it's unclear how effective Amazon is at proactively policing these rules.

Still, the spokesperson said that if Amazon does find a product that doesn't meet its guidelines, it is quickly removed.

"If customers have concerns about items they've purchased, we encourage them to contact our Customer Service directly to investigate and take appropriate action," he said.

This isn't the first time Amazon has come under scrutiny for the items sold through its marketplace, its vast network of third-party sellers which sell and distribute items through the Amazon network.

In September, a Wall Street Journal report revealed that thousands of items sold on its site were not deemed safe by regulators. Most concerningly, these items included children's toys and medication for adults.

Read more: Amazon was caught selling thousands of items that have been declared unsafe by federal agencies

CNBC put together its investigation with help from data analytics firm 3PM.

3PM's chief product officer Jon Derkits – who worked at Amazon until June managing the third-party consumer electronics division – told CNBC that Amazon was addressing these food expiry issues but that there were still "big gaps" in its inability to prevent customers from receiving out-of-date goods.

"They hadn't yet earned my trust, as either an Amazon employee or a customer, that I would be safe purchasing a consumable or expiration-dated product from a third-party seller," he told CNBC.

Read the full report from CNBC here.