I bought an open-item, unregistered MacBook Pro from Best Buy and they told me that they had installed Mountain Lion just like a clean setup. But the iLife bundle doesn't appear in the laptop or in the App Store (the "Purchased" section is empty). Does anyone know if I need to buy it?
Best Buy lied. When they reinstalled the machine, it wiped iLife. Here's what you need to do, from http://forums.macrumors.com/showthread.php?t=1224880
The answer is regrettably yes, you have to buy it. Unless you get lucky.
I went through this experience when I bought my open-box MacBook Air from Best Buy. At first I thought that I could contact Apple Support and get them to attribute the software to my Apple ID, but I was wrong.
The free copy of iLife that comes with every new Mac is given to the first Apple ID that gets associated with a user account on the Mac. It's non-transferrable, because it's somehow tied to the hardware (I don't know the details).
However, fortune smiled upon me. When I upgraded from Lion to Mountain Lion, a firmware update or something gave me the ability to download the iLife suite for free. It seems that an OS upgrade or certain updates can post-link the apps to your Apple ID.
Summary: I recommend only buying the iLife apps that you need. Wait and see if a future update brings you the others.