needs reset/wiped

I have actually used this method in this link:

https://www.macworld.co.uk/how-to/mac/forgotten-mac-password-3594395/

Are you implying that the computer is locked at the boot up screen or account screen? I would suggest you to wipe the computer by utilizing macOS Recovery, accessible by holding down ALT while booting up. However, since you purchased this unit from an estate sell, I have a strong feeling that the unit is locked to the iCloud account of the original user. If necessary, take the unit to Apple Store for further procedures.

Unless you need the data and/or applications of the current user, I would just go ahead and wipe it.  

Boot while holding down CMD-R to access the Recovery boot drive directly.  If that should not work, reboot while holding down the Option (ALT) key.  That should bring up a boot menu, allowing to choose which option from which to boot the computer.  Choose the Recovery option if available.  If it does not exist, you will need an external USB key that is bootable and has an installer on it.

You will then be able to set up your own Apple ID and make your own purchases.

As to taking it to the Apple Store, they might be able to provide a bootable key or perform the wipe themselves.  Other than that, I'm not sure what else they can do under the circumstances.  They will need proof of purchase at the very least and might ask for proof that you have the rights to access someone else's Apple ID (iCloud, App Store purchases, etc.)  I would imagine that they would tell you to wipe it and start over in the manner I outlined above.

Since you mention an Estate Sale, it may be an older Mac.

That command r only work on the newer Macs.  If it's a much older Mac, boot into Single user mode by holding down command s

fsck -fy
mount -uw /
rm /var/db/.AppleSetupDone
exit

This will reset the Mac to start the new Mac setup program.
Log in and set up the new admin account.  Once logged in, delete all the old programs and users account that you can.  You'll eventually need to open terminal and remove any previous user accounts
sudo rm -rf /Users/{List,of,old,user,folders}

Once that's done write zeros to the empty spaces on the disk to prevent casual recovery.  Let it fill the disk and remove the file.
cat /dev/zero > zerofile; rm zerofile
If you have a really old Mac HFS disk, you may have to write a loop and let it write multiple 2GB files, then remove them.

I just write a single pass of zeros.  That's sufficient enough to prevent all simple recovery software from access.  You only need to do the DoD wipe if you expect someone to send it to DriveSavers or some such company that can read between the standard tracks to do forensic recovery.  

If you want to be a bit more secure.
cat /dev/urandom > Pseudo_random ; rm Pseudo_random

Be sure to use urandom and not random or you'll spend up to 3 times longer.  This will take about 5 times long as long as writing /dev/zero.

Alternate the writes a few times and you can replicate a DoD wipe.

When you're done, remove the setup file.
sudo rm /var/db/.AppleSetupDone