Amazon's Prime Big Deal Days can be an excellent time for bargain shopping. Whether you're using it to get a few essentials at a discount or hoping for a good deal on a big purchase, you can come across some great money-saving opportunities.

That said, it would be a mistake to assume a discount always equals a deal when it comes to Amazon's autumn sale, which runs from Oct 10-11. CNBC Select explains how to make sure you're really getting a bargain when you buy this fall.

When you see a discount on Amazon, you assume you're buying the item for a lower price than what it normally sells for. But in fact, you might not always be getting the best deal.

A study published last year found that third-party sellers on Amazon can sometimes raise base prices before a sale, and then during the sale advertise a discounted price that might be the same or higher than the base price was before it was hiked. This creates an illusion of a deal when in reality, you'd be paying the same as before — if not more.

The data for the study was gathered during a 13-month period in 2016 and 2017. "Since that time we have introduced and continuously improved a series of robust mechanisms to prevent, detect, and stop the kind of actions from our selling partners discussed in the report," says Amazon spokesperson Maria Boschetti.

Still, it's natural for prices to fluctuate, so researching the deals you find during Prime Big Deal Days (or any other sale) is always a good idea if you want to find the best price possible.

Naturally, to know whether the price of that hair dryer or set of headphones has increased during the run-up to Prime Big Deal Days, you need to track it. You can do this manually, but that requires you to know months in advance the specific items you'll want to buy (not to mention the tedious labor of checking the prices and logging them).

Luckily, you can use tools to guide your decisions and avoid manual tracking. Some browser extensions can make price tracking a simple process. For example, camelcamelcamel monitors prices on millions of products on Amazon. You can also view price history charts to get an idea of price changes over time. And if you get The Camelizer, a browser extension that comes with the service, you can access the charts right in your browser.

Checking price history and applying coupons can help you ensure you're getting the proper bang for your buck during Prime Big Deal Days. If you want to prepare even more for the sales event, you can look into a couple of other tools to take your shopping experience (and savings) to the next level.

First, remember that while it's an Amazon sale, you might be able to find a lower price elsewhere — be open to that idea. Tools also exist to aid your search for a better deal. We recommend downloading Capital One Shopping, which you can do even if you don't have a Capital One credit card. Capital One Shopping is an app, as well as a browser extension. Like Honey, it can automatically apply coupons at checkout, but it also lets you compare prices at different retailers.

If you add the browser extension, you'll see a button in Amazon product details letting you know whether you're getting the best deal. If not, you can click the button and Capital One Shopping will take you to a page with more information. Here, you'll see how much other retailers charge for the same item, including shipping and other fees, and get direct links to shop.

Speaking of credit cards, the right one can help you save money on Amazon regardless of whether it's Prime Day. For example, CNBC Select picked Prime Visa as the best card for Prime members since it offers 5% cash back at Amazon.com, as well as at Whole Foods Market. Additionally, you'll get 5% back on purchases made through Chase Travel (since it's a Chase card), 2% back on local transit and commuting, including rideshare, 2% back at restaurants, gas stations and drugstores and 1% back on all other purchases. Plus, you can receive a $200 Amazon gift card upon approval. The card has a $0 annual fee, but you'll need an Amazon Prime membership to take advantage of the elevated rewards rates and gift card offer.

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At CNBC Select, our mission is to provide our readers with high-quality service journalism and comprehensive consumer advice so they can make informed decisions with their money. Every personal finance guide is based on rigorous reporting by our team of expert writers and editors with extensive knowledge of financial products. While CNBC Select earns a commission from affiliate partners on many offers and links, we create all our content without input from our commercial team or any outside third parties, and we pride ourselves on our journalistic standards and ethics. See our methodology for more information on how we choose the best products.

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