3 All-Too-Common Mistakes People Make at Costco That Cost Money

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Costco isn't one of those stores where you typically go to pick up one or two things. For many of us, a Costco shopping run is a major haul -- one that leads to a heaping shopping cart and a reasonably large credit card bill to follow, even when we account for the store's competitive prices.

Because of this, it's important to approach your Costco shopping strategically. And that means avoiding these all-too-common mistakes that could end up hurting you financially.

1. Buying bulk products that end up going to waste

One of the primary draws of joining Costco is getting to save money on bulk grocery purchases. When you buy a massive carton of blueberries instead of just a pint like you would at the supermarket, you're typically paying much less per ounce -- or per berry -- as just one example.

But the savings you reap from Costco's bulk offerings can be seriously wiped out if you end up throwing food away consistently due to not being able to finish it before it expires. If that's a trap you've been falling into, you're wasting your money repeatedly. So it's time to break that cycle, which means you should no longer be buying items your household is incapable of finishing before they go bad.

To be clear, this doesn't mean you have to say goodbye to bulk buying at Costco in general. Rather, if you typically buy cheddar cheese in bulk only to have half the package get moldy before you finish it, then cheddar cheese is one specific item to take off your Costco shopping list.

2. Not paying attention to the store's return policy

For the most part, Costco will let you bring back any item for any reason for a complete refund. But there are exceptions to this rule, and it's important to know what they are.

Failing to familiarize yourself with Costco's return policy could cause you to get stuck with purchases you don't want or need. The result? Throwing away money.

Items that cannot be returned to Costco include:

• Cigarettes
• Alcohol
• Event tickets
• Gift cards
• Gold bars
• Silver coins

Meanwhile, certain products have a limited return window. With electronics, you get 90 days to make a return. And that rule extends to major appliances, too.

3. Choosing the wrong membership tier

Choosing the wrong membership tier based on your Costco shopping habits could cost you money -- either because you're overpaying for a more expensive membership unnecessarily, or because you're missing out on the cash back you can get from a higher-cost membership.

Costco's basic membership costs $60 a year right now, while the Executive membership costs $120. In September, these fees will rise to $65 and $130, respectively.

If you only shop at Costco a few times a year, you may not earn enough cash back from an Executive membership to make back the cost of the upgrade. So that's one way the wrong membership tier might cost you money. But the opposite also holds true in that if you shop at Costco often but limit yourself to a basic membership, you might miss out on earning cash back that exceeds the cost of an Executive membership upgrade.

Based on the current fee structure, it takes $3,000 in annual Costco spending to break even on the cost of an Executive membership upgrade. Come September, it will take $3,250.

But if you typically spend $5,000 a year at Costco, that means you could be earning $100 cash back with an Executive membership. So even once the price rises to $130, marking a $65 difference between Costco's two tier choices, if you're able to score $100, you're ahead by $35.

Shopping at Costco has the potential to be a huge money-saver. But avoid these blunders along the way to make the most of your membership.

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