How to buy a used Mac without being locked out

One of the great selling points for Macs has been a combination of their longevity and resale value. I know plenty of people with decade-old Macs. In the last two decades, I’ve easily gotten seven or eight years out of some Macs I’ve owned, and then sold them to folks who kept them in service.

There’s a lot to consider when buying a used Mac to make sure that it will keep working. But something that you might overlook is that security decisions made by the previous owner could conspire to lock you out in certain circumstances. This could happen on a restart, when trying to erase and reinstall macOS, or even on logging in, depending on what state the Mac was left in when you purchased it.

The best way to buy a Mac is after the seller has erased the drive and installed a fresh copy of macOS on it without yet completing setup, so you can do that from scratch without worrying about any software they may have installed or passwords or accounts they’ve created.

And the best scenario to receive a used Mac is to do so in person, so you can fire up the computer and see it’s working, run through tests listed below, and be sure no extra passwords or permissions are needed.

Regardless of how you receive the Mac, check out these items—preferably before finalizing the deal.

  • Shut the Mac down and perform a “cold boot”—start it up and see if you can log in with account information provided or complete macOS setup.

  • Restart normally from the Finder and hold down Command-R to make sure you can start up in macOS Recovery. (If macOS Recovery isn’t installed, the Mac should attempt to retrieve it over the internet and install it. If shown a lock icon and password field by itself, see the firmware password section below.)

  • In Recovery, run Disk Utility. Can you mount the disk without a password? And run Disk First Aid to ensure that no problems are reported.

That covers the basics, but you can and should dig deeper. (You should also use this checklist before selling a Mac.)

Tip: If a seller balks at providing a password to you directly for something that can be typed in while booted into macOS proper—a perfectly reasonable thing to resist—you can use a slightly hidden feature for iMessages. In a chat session with Messages for macOS that has the blue bubbles showing an iMessage connection, click the Details button in the upper-right corner, and then click the overlapping screens icon. Select Invite to Share My Screen. The seller can then remotely type the password in as required. (They may want to and probably should change their iCloud or other password after that, too.)

Were one or more accounts created?

If someone else set up a computer, you don’t necessarily know what’s running on it. I suggest erasing the drive and reinstalling macOS via macOS Recovery. However, if that’s not an option or you’re not concerned, at least delete all unnecessary accounts and change the password on the main account, which must have administrator privileges.