eBay lingo explained

"Pulled from a working system"

working  =  I turned the system on, and I either heard the power supply fan turning, or I saw a light somewhere turn on.  No smoke was evident.

"It was working the last time I powered it on"

Meaning #1: It does not work now.  I will say that it it worked the last time I powered it on.  When the buyer complains, I will say that it was working 5 years ago, and must have deteriorated in that time.
Meaning #2: I have no idea how to tell if it is working or not.  But, I think there's a good chance that it is working.  I do not want to list it as untested because that will put a lot of people off.  I will list it as, "It was working the last time I powered it on", and take my chances.

"extremely rare"

Example:  I would list one of my toenail clippings as extremely rare, because only my clippings contain my DNA.

"includes a certificate of authenticity"

Includes an authentic certificate.