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Don't make these 6 common mistakes and do Amazon Prime Day right

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For online shoppers, Amazon's Prime Day on July 16 has become as highly anticipated as Cyber Monday. For Amazon, it's been even more successful.

This year, the sales start at 3 PM Eastern time and continue for 36 hours until Tuesday night, making for the longest and most globally accessible Prime "day" yet. There will be "more than one million deals exclusively for Prime members," according to the company.

Jeff Bezos's e-commerce giant continues to dominate online retail: Amazon is expected to take nearly half of the U.S. e-commerce market by the end of the year, according to a recent report by analysts at eMarketer.

To get the most out of the sales event, here are some common mistakes to avoid when shopping on Prime Day.

1. Paying $119 for Prime to participate

Yes, Prime Day is only for Amazon subscribers, but if you're not one, don't think you have to pay the $119 yearly fee to take part. New subscribers can sign up for a 30-day free trial and get access to the deals.

But remember to read the fine print. At the end of the trial, Amazon will automatically upgrade you to a paid membership plan. You have to affirmatively turn off the automatic renewal before the end of the trial if you don't want to get charged.

2. Forgetting to check your Amazon account beforehand

Make sure your credit card info, account and shipping info are up to date. With limited sales, time is of the essence. Don't discover you have to update your expired credit card in the middle of a purchase.

3. Falling down the Prime Day rabbit hole

"Part of the challenge on Prime Day is that are are so many products that can be discounted," says Rick Broida, CNET's online deal expert and author of blog The Cheapskate.

For that reason, online shopping expert Michelle Madhok suggests having a game plan that focuses on only what you need. Or, she advises, "sometimes the best thing you can do is go for a big ticket item."

Even if you drill down toward something specific, the number of products is huge, says Broida, so download the Amazon app and enable alerts. With deals posted every five minutes, it's the best way to keep track.

4. Assuming Prime Day has the best prices

"Not every deal that you are going to see is going to be the best deal in the history of deals," Broida tells CNBC. Amazon products, like Echo Dot and Alexa, will see some of the deepest price cuts, as will tech and electronics.

To know if you're really getting a great deal, Broida suggests an online tool "amusingly called camelcamelcamel.com. You can copy and paste the link from Amazon and see the price history for that product."

Other retailers have noted the success of Prime Day and created their own July sales to lure away some of Amazon's bargain shoppers. "[T]he only way [other big box retailers] will draw attention away from Amazon is through great deals," PwC's Consumer Markets lead Steve Barr told CNBC in 2017. Retailers like Target, Macy's and Walmart are all offering deals too.

5. Not taking advantage of the wait list

Is what you want already sold out? Some deals have a wait list feature. It's worth the click because shoppers often put items in their carts but change their minds before checkout, says Broida, so "you will be notified if it is available again."

6. Making impulse purchases

To avoid overspending, April Benson, Ph.D., the author of “To Buy or Not to Buy: Why We Overshop and How to Stop” tells CNBC you should ask yourself six questions: Why am I here? How do I feel? Do I need this? What if I wait? How will I pay for it? Where will I put it?

If you have good answers, "then it is probably not an impulse purchase,” Benson says.

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This is an updated version of a previously published article. It has been corrected to reflect the current price of an Amazon Prime membership.