Factory reset not clearing hard drive?

[Unprocessed1]

I'm trying to erase all data and factory reset a mid 16 MBP with SSD to get ready to sell it. When I went to disk utility to erase the data, the process only took less than a minute and I noticed there was only 35gb left of free space on the 256gb ssd. It still removes my accounts and I'm now reinstalling OSX.

Was there a problem with the process, and would my old data still be on the computer

NOTE: the screenshot is from after erasing. Now erasing the hard drive again is not an option. (Greyed out)

 

[Unprocessed1]

Now installing MacOS Sierra results in an error message after several minutes (the estimated time actually reaches negative seconds before it happens). What a nightmare.

 

[Fishrrman]

Time to start over.

Do it this way:
PRINT OUT THIS MSG and keep it for reference.

- Power down, all the way off
- Reboot to INTERNET RECOVERY (NOT to "the recovery partition"):
Command-OPTION-R
- You'll need your wifi password and it will take some time to load. BE PATIENT.
- When you get to the internet utilities, open disk utility
- IMPORTANT! Go to the "view" menu and choose "show all devices".
- NOW you should be able to see "the top line on the left" that represents your internal hard drive. Click on it to select it.
- Erase the ENTIRE drive to APFS, GUID partition format.
- Now you should be able to quit disk utility, open the installer, and install the OS.

 

[Unprocessed1]

Thanks for your help. That seems to have wiped my hard drive successfully. Installing Mac OS now

Time to start over.

Do it this way:
PRINT OUT THIS MSG and keep it for reference.

- Power down, all the way off
- Reboot to INTERNET RECOVERY (NOT to "the recovery partition"):
Command-OPTION-R
- You'll need your wifi password and it will take some time to load. BE PATIENT.
- When you get to the internet utilities, open disk utility
- IMPORTANT! Go to the "view" menu and choose "show all devices".
- NOW you should be able to see "the top line on the left" that represents your internal hard drive. Click on it to select it.
- Erase the ENTIRE drive to APFS, GUID partition format.
- Now you should be able to quit disk utility, open the installer, and install the OS.