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Since Amazon's acquisition of Whole Foods, it has become a dominant grocery marketplace. However, thousands of reviews on food items point out the inability of Amazon to monitor the quality of food products being sold by third-party vendors.

Amazon customers have to identify counterfeit and unsafe products when purchasing items from Amazon. The A to Z guarantee provided by the company is supposed to keep customers safe from ending up with expired or unsafe food products. However, reviews on the website reveal that third party sellers are shipping off expired or near-expiry products to customers.

Amazon policy allows sellers to sell products that have at least 90 days of shelf life left from the time of shipping. However, sellers buy products en masse from closeout sales and liquidation warehouses. Products like Starbucks' Teavana items are still available for sale on Amazon, even though Starbucks shut down Teavana two years ago. Customers who have bought the products claim that they have a chemical smell.

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Amazon grocery delivery service trucks Getty Images/Kevork Djansezian

Not only are sellers selling stale products, they are also selling counterfeit consumables. Customers who bought Fiji water wrote reviews saying that they got used Fiji water bottles which were filled with regular tap water.

CNBC hired data firm 3PM to analyse the customer complaints received by Amazon's 100 best-selling products. The data dig pointed out that 40% of the sellers have more than five customer complaints regarding the product they have sold.

Michael Neuwirth, a spokesman for French food group Danone, pointed out that the sale of expired or unsafe consumables ends up hurting two parties. The irresponsible behaviour from the sellers harms the customers as well as the manufacturer. It is the reputation of the brand which is getting damaged when customers receive a rotten product.

Many manufacturers like Southwest Specialty Foods and Abbott Laboratories have taken steps to warn customers about buying their products from third-party sellers. They have also hired teams to regulate the sale of their products, to ensure that sellers do not have large batches of the products sitting around.

As a response to the growing concern over the issue, Amazon released a statement which claimed that they use artificial intelligence as well as a manual process to ensure product quality. The company also stated that it went through over 22 million reviews each week to monitor the products being sold by their third-party vendors. The statement encouraged customers to reach out to Customer Service if they face an issue with any of the products sold on the site.