Do not buy StarCraft II used. You will not be able to play.
StarCraft II is only playable via a Battle.net account with rights to play StarCraft II. There are 2 ways to get those rights:
- Purchase the game online via the Battle.net website.
- Purchase a boxed copy of the game and register the 1-time use key with your account on the Battle.net website
If you do purchase the boxed copy used, the 1-time use key will probably already have been used.
The only thing you could possibly hope to get from purchasing the game used is any of the physical media that comes in the box (the manual, the disc itself). If you haven't purchased the game already, chances are you don't care one whit about any of that stuff anyway.
Edit: @mousey adds that the key has not been used. If that's actually the case, technically you should be able to play it if you do get it. However, it's mostly against the End User License Agreement as stated in the manual:
No Transfer or Sublicense. THE GAME IS LICENSED, NOT SOLD. NEITHER
THE GAME NOR THE LICENSE GRANTED IN
SECTION 1 MAY BE SUBLICENSED OR
TRANSFERRED TO ANY OTHER PERSON OR
ENTITY, AND ANY ATTEMPT TO DO SO
SHALL BE NULL AND VOID. If a court of
competent jurisdiction finds the
foregoing sentence to be
unenforceable, you agree that you will
call Blizzard Customer Service at
1-800-592-5499 to arrange for the
transfer of your rights under this
Agreement to another person with a
valid Battle.net account; provided,
however, that Blizzard may charge a
processing/handling fee to facilitate
the transfer, issue a unique key to
the transferee, and remove the
preexisting key from the Battle.net
account registered to you.account registered to you.
So it sounds like the seller is breaking the rules anyway unless he has actually contacted Blizzard about it. Not that I'm a EULA expert.
Personally, I would buy the game new. But I am incredibly biased because StarCraft II is pretty much my favorite game ever.
I'll take heed to the subjective nature of this question but I'll share my speculative answer anyway.
At the time of writing this the engineering bay costs 125 minerals, takes only 35 seconds to create, has 850 health and has +1 armor. If the engineering bay could lift off, you could have a pretty durable scout that's fast and cheap to create. This could open up a whole slew of possibilities for Terran.
Best Answer
A straight copy-paste of the whole installation folder should work. If you want to copy user-specific data as well, it should be in (My) Documents/Starcraft II.
Blizzard is actually really good about making their installations copy/pastable. Don't remember about the original Starcraft, but Warcraft III, WoW and SC2 can all be moved by just copy/paste on the whole installation directory. Any registry stuff is recreated on the new machine if it doesn't already exist (Not sure if it's updated if there's an old installation)