Bought a used MacBook and I wanted to do a factory reset. Now it’s not allowing me to log in

It seems the seller did not properly prepare this Mac for sale. Here is what the seller should have done prior to selling the Mac:

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

Personally I would immediately return the laptop for a full refund since this Mac was not properly prepared for sale. A Mac not properly prepared for sale could contain a firmware lock or even still be managed by a previous owner (maybe even an owner previous the the current seller). It is easy to check for a firmware lock as holding the Option key immediately after the startup chime will show a padlock on the center of the screen (only for Intel Macs). If a firmware lock is enabled, then there is no way you can remove it.

As far as the laptop being managed by a previous owner, that may not be as easily discerned. Many times when performing a clean install, you will see a notice during initial setup about the laptop being managed, but there are ways to avoid this from being shown, but sooner or later macOS will nag you about the laptop being managed by a previous owner....this could take days or weeks before you may receive a notice.

The fact that the seller is not communicating is also a big red flag screaming "Danger!".

What is the exact model of this Mac? You can get this information by entering the system serial number here:

Check Your Service and Support Coverage - Apple Support

FYI, even if the seller did properly prepare the computer for sale, I always recommend that the new owner performs their own clean install of the OS to the device so they are absolutely certain that the OS is a clean factory fresh installation...you never know what nasty surprises the previous owner may have left behind (intentionally or accidentally).

Assuming there is no firmware lock on an Intel Mac and the laptop is not still being managed by a previous owner (Intel or Apple Silicon), then it should be possible for you to perform a clean install of macOS on this laptop without requiring any passwords from the previous owner. A clean install means erasing the drive (or actually the "Volume Group" on newer systems), or if it is a 2018+ Mac, then performing a firmware "Restore" is the best option as it will also reset the security enclave as well, but the "Restore" does require access to another Mac running macOS 10.15+.

How to reinstall macOS - Apple Support (must click the link for "erase" within the relevant article for how to delete the Volume Group in order to erase the Mac for the "clean" install)

Revive or restore a Mac with Apple silicon using Apple Configurator - Apple Support

Revive or restore an Intel-based Mac using Apple Configurator - Apple Support

FYI, it is extremely risky buying a used Mac from an unknown seller. Sometimes even known sellers may have these issues as well. Buyer beware when buying used electronics these days.

Hello Jphillip95,

You've come to a great place for help with setting up the Mac. To confirm, are you seeing a screen with a folder and question mark? If so, you'll want to complete the steps listed below as they're specific to resolving this issue. you can also find these steps outlined in the following article.

1. "Press and hold the power button on your Mac for up to 10 seconds, until your Mac turns off. Every Mac has a power button. On notebook computers that have Touch ID, press and hold Touch ID.
2. Use Disk Utility to repair your startup disk. Follow the steps for a Mac with an Intel processor.
3. If Disk Utility found no errors or repaired all errors, reinstall macOS.
4. If you still need help, please contact Apple Support."

If your Mac starts up to a question mark - Apple Support

If you're having a different issue, please let us know in more detail about the issue you're facing. The more detailed the explanation, the more accurate our troubleshooting steps will be.

Have a great day!