4 Costco Mistakes That Could Cost You Big Time

Many people join Costco to achieve one primary goal -- save money. And hey, that's a really important goal to attain. But if you fall victim to these mistakes, you might cost yourself money rather than save some.

1. Buying everything online

Shopping at Costco.com might seem like a more appealing option than visiting the store. You don't have to get in your car and make the drive, and you don't have to battle any crowds.

But you should know that generally speaking, you'll pay more for items you buy on Costco's website than you will in the store. There can be exceptions, but this is generally what you'll find. So if you're trying to cut down on household spending, shopping only online might hurt you.

One advantage of Costco.com is that you might find a wider range of products than at your local warehouse club store. But if it's a larger purchase you're making, do yourself a favor and compare the cost online versus in-store before you complete it. There's no sense in paying $1,200 for a TV online, for example, when you can potentially pay $1,150 at the store.

2. Not trying the free samples

You may be inclined to pass up Costco's free samples to avoid coming off as greedy. Or maybe you just don't want to wait in line to get a free slice of cheese or bite of granola, and that's understandable, too.

But the nice thing about the free samples is that they let you know if a given food item is something you actually enjoy. If you take a chance on a new type of granola cluster because you think it looks delicious based on the box, only to find that it actually tastes like it was wrapped in tree bark, you'll potentially end up wasting your money by dumping your large-sized bag once you've busted into it.

Instead, try a sample when it's a new item you're thinking of buying. And if you're not sure after one free sample, ask for a second. You're totally allowed. 

3. Assuming an Executive membership won't pay off

A basic Costco membership costs $60 a year, while an Executive membership costs $120. An Executive membership gives you 2% cash back on all Costco purchases. But if you don't tend to shop at Costco a lot, you might assume that a basic membership makes more sense.

It only takes $3,000 in annual Costco spending to break even on the extra $60 you're spending on an Executive membership. So a single large purchase -- such as if you buy furniture or book a trip through Costco Travel -- could push you over that limit, even if you only shop at the store for things like groceries a few times a year. 

4. Forgetting to fill up gas on your way in or out

Costco gas is often a lot cheaper than other stations. Of course, it's a good idea to look around your neighborhood and verify that this is true. But if it is, try to remember to fill up your car at Costco before or after you do your shopping (you may want to stick to "before" if you tend to buy a lot of perishables so they don't have to sit in your car for longer). 

If a Costco gas fill-up saves you $1 each time, and you fill up there pretty much every week, you can bank an extra $50 a year. That's practically the cost of a basic membership right there.

A Costco membership could do a lot of good things for you. But try to avoid these mistakes so you don't miss out on savings opportunities.