Can't erase Macintosh HD (FileVault active)

1. once installed and the machine has rebooted, i assume it'll prompt me for the user setup. i seem to remember that pressing cmd-Q will let me quit the installer.

Yes, the Mac will behave as if it came from the factory and will prompt to set up an initial user account.

2. but in that case, if the potential buyer wants to try my MBA, he/she needs to enter his/her credentials, otherwise this isn't possible, is that right?

You could allow it to go through and setup any dummy admin account. Just don't make changes to the drive such as adding software or deleting anything. Once sold, the new owner can enter the current admin account, create a new admin account for themselves, then login to that and delete the dummy account.

I'd do what Kurt suggested: in order for a potential buyer to try it, they'd need access of course. I've usually set up an account "admin", password: 1 2 3 4 5 so they can try it. I tell them how to reinstall so they can start over and set up their own account.

Of course it's cool to stop the install so the buyer gets the new setup screen, but then they can't test it......

And I'm glad to hear internet recovery is doing what it is supposed to do.....

Good to hear!

Attn. Topher

Terminal method did not work.

When follow directions, I received this after input of UUID number

Usage: diskutil coreStorage delete lvgUUID

Deelte a CoreStorage logical volume group. All logical volumes will be removed.

Ownership of the affected disk is required.

I checked premissions under info on the harddrive, but the Ignore Premissions box was checked.

I added my user name to the list able Read & Write but same results.

Is there an extra step missing?

P. S. Found a working solution elsewhere.

Type sudo diskutil cs deleteLVG

followed by the UUID number