The most expensive mistake you can make buying a used Mac isn’t a bad battery. It’s a machine that’s still tied to someone else. It looks fine in the photos, boots fine, and then asks for a password that isn’t yours.
There are two ways a Mac can be locked, and they’re different problems.
Activation Lock is personal. It’s Find My. The Mac is tied to the previous owner’s Apple Account, and after an erase it will ask for their password before it does anything else. Only they, or Apple with proof of purchase, can remove it.
Remote management, MDM, is corporate. The Mac was enrolled in a company’s device management, and enrolment survives an erase. You can wipe it ten times and it will still phone home to a company that no longer employs the person who sold it to you. Only that company can release it.
If you’re checking a machine yourself
This only works if the Mac is physically in front of you and switched on.
First, look in System Settings for the previous owner’s account. They need to be signed out, and Find My needs to be off. Then go to General, then Device Management, and make sure the list is empty. Then, and this is the one that matters, erase the machine in front of the seller and run Setup Assistant. If it asks for someone else’s Apple Account, or shows an enrolment screen with a company name on it, don’t pay.
Ask for the serial number in advance too. Apple’s coverage page tells you the warranty status, which also tells you whether the machine is roughly the age the seller claims.
None of this is possible when the Mac is being posted to you. Which is most of the time.
What we do instead
Both checks happen on our intake bench, before the machine is listed. We erase it, run Setup Assistant, and confirm that neither lock is present. The result goes in the Device Passport on the product page, per unit. You don’t need to ask, and you don’t need to check it yourself when the box arrives.
Questions we get
Can Activation Lock be removed without the previous owner?
No. Anyone offering to do it for a fee is either lying or working with stolen machines. Walk away from both.
I erased the Mac. Is MDM gone now?
No. That’s the point of MDM: it comes back after a wipe. Only the organisation that enrolled the device can release it.
Do you actually check both before listing?
Yes, on every machine. If we ever ship one that’s locked, that’s on us: 24 months of warranty and 14 days to return it.