Will a buyer be able to recover my files if I format my mac HD and sell it? If I follow the standard procedure for logging out and formatting my Mac before selling it, as described in https://support.apple.com/en-us/HT201065 - Will the buyer be able to recover my files with forensic software ? Who is liable if the buyer can recover personal files with sensitive information, given that I followed the instructions given by support ? 

If the buyer is able to retrieve info with forensic tools - why do I almost have to be a computer scientist to understand how to sell my computer safely ? 

Is a user friendly deep format too much to ask ?
The accepted procedure these days is that you already have FileVault enabled, right from the first time you use the Mac.

If you do, then the simple format &amp; reinstall in Apple's instructions is totally adequate to prevent any recovery.

If you don't use FileVault, then there is no proven * method to make your data absolutely * irrecoverable.

Therefore, if you don't already use FileVault, enable it first across the entire drive. Wait until it finishes encrypting your data [may be days], then follow the simple format/install instructions.
This is not as quite * as secure as if the drive had always been encrypted, but as good as any "secure erase" procedure.
For practical purposes SSDs are safer * than HDs.

*words in italics would take 20 pages to fully explain.