Substantial amount of missing storage. Refurbished MacBook Air M2 only has 150 GB SSD despite buying it from the listed amount of 512GB SSD.

Buying used Macs from resellers is always a gamble, generally not recommended (due to stories like yours) unless you are buying refurbished products from Apple or from OWC. Things don't arrive as expected, often. With Apple and OWC, you get a warranty and window for returns. Also, Apple refurbished products generally arrive in like-new condition, exactly as described.

In your case, you should either return the device immediately, or if you want to try to make it a go, following these instructions EXACTLY:

What to do before you sell, give away, trade in, or recycle your Mac - Apple Support

This procedure will completely erase your drive and recover all space on it. If you still don't see 512 GB then you have been taken advantage of, and your only recourse is to return the computer.

Offhand comment: I think I would be especially leery of buying from a reseller calling itself "ItsWorthMore."

Also ... is this an Amazon Renewed product? If so, Amazon says: "We want you to be delighted with your purchase. If the product does not look or work as expected, you are eligible for a replacement or refund within 90 days of receipt with the Amazon Renewed guarantee."

If I were you, I would go for the refund. Also, "acceptable condition" is the lowest grade Amazon gives for used computer sales.

Return it and get your money back.

"Substantial amount of missing storage. Refurbished MacBook Air M2 only has 150 GB SSD despite buying it from the listed amount of 512GB SSD."

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Clear the System Data:

See that middle-color gray line on your Mac's hard drive bar? That is System Data, all of which can be deleted, without having any affect on your Mac's files. Use my User Tip for that: How to Use Finder to Clear “System Data" on a Mac - User Tip. It can take some time, so e certain you have the time to do so.

Screenshot:

System Data pointed to with red:

bathingape64 wrote:

I asked ChatGPT, and it helped me resolve my problem and restore the original amount of storage. However, please know that I appreciate your consideration and suggestion.

May I ask what you had to do to resolve the issue?

I have an inquiring mind.

Even though you may have "fixed" the issue, I highly recommend you follow the advice provided by @steve626 and properly erase & set up the computer again (begin with Step#5).

Personally if it were my computer I would go even further and perform a DFU Firmware Restore on it, but that would require access to another Mac running macOS 15.7+ Sequoia or macOS 26.x Tahoe.

Good computering. Thank you. 👍🏽