Amazon works with lots of third-party sellers, but the retail giant wants customers to know it still has you covered.

The purchase of Whole Foods not only got Amazon deeper into the grocery game, acquiring the respected brand also beefed up Amazon's grocery bona fides. But even if you are more likely to associate Amazon with a supermarket than you were a couple years ago, the greater Amazon marketplace is a very different beast: less like a grocery store and more like a market hall, where individual vendors can sell goods with limited real-time oversight. For customers, Amazon's multiple methods for selling stuff can prove confusing, and according to a recent CNBC report, unsavory sellers have been slipping expired food items into the system.

After hearing complaints of Amazon customers being sold expired goods, CNBC enlisted help from the data firm 3PM which discovered that at least 40 percent of the sellers of Amazon's 100 best-selling food items had over five complaints about expired goods—everything from year-old Hostess Mini Brownies to Teavana tea clearly marked "not for resale."

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Precisely how prevalent the problem is hard to say, but that's part of the issue: Amazon reportedly deals with over 2.5 million independent retailers (only some of which offer food items) who sell through the site: Monitoring that many businesses is a herculean task. "Our top priority is ensuring customers receive safe, high quality products when they order from our store," an Amazon spokesperson told me via email. "We require all selling partners to abide by strict product quality guidelines. We have proactive processes in place to ensure customers receive products with sufficient shelf life, and use a combination of artificial intelligence and manual systems to monitor for product quality and safety concerns in our store. If we find a product doesn't meet our guidelines, we remove it from sale and take appropriate action against the seller, which may include removal of their account."

More importantly, Amazon says if you do receive any expired goods, it wants you to know that you are covered with a full refund—as long as you actually reach out to tell them there was a problem. "If customers have concerns about items they've purchased, we encourage them to contact our Customer Service directly to investigate and take appropriate action," the spokesperson continued. "Our customer service teams are empowered to instantly stop sales of an item if there are quality concerns. With the A-to-Z Guarantee, customers are protected and will receive a refund if they have issues with a product, whether they make a purchase from Amazon or a third-party seller."

Meanwhile, if you're still feeling unsure about a purchase, you can take further steps yourself. As much as Amazon streamlines the purchase of items so you can simply click and buy, the company does provide additional info if you're willing to dig. Every page has a link to seller information that also notes whether the order is fulfilled by Amazon or the third party seller. (Amazon handles customer service on the items it fulfills, so in theory, you should receive more reliable customer service in those situations.) You can also look at the reviews of the sellers themselves to see what kind of feedback they've received and sometimes even choose a specific seller you'd like to buy from—though pricing may vary.

In the end, it's important to remember what Amazon is and what it isn't. Yes, Amazon sells stuff itself, but, often, the company is just the middleman. The bad news is that, just like buying stuff at a farmers' market, Amazon hasn't necessarily been able to check every vendor every single day. But the good news is that Amazon says it wants to resolve any issues you have. Yes, it might be a bit of an inconvenience—but it's just part of the territory that comes with not having to leave your house to buy stuff.