How can I tell if a cabinet's speaker is blown?

[ColinDeacon]

I am about to buy a used Gallien-Krueger Backline 600 300W head and an 8X10 Backline 800W cabinet. I went to test it out and it seemed to me that it wasn't very loud and I couldn't turn the volume up to the high levels because the sound would distort.
How can I tell if an amp's speaker is blown? Or what else should I take into consideration?

Thank you for your help!

 

[Kitsapbass]

Unscrew the grill, push lightly on the speaker cone itself. If you hear a scratchy sound, speaker is toast...is it a private sale or a place like GC?

 

[ColinDeacon]

Thank you. It's a private sale.

 

[Marko 1]

Might be the cab itself.

I have a cab (212) that I drove really hard for a while, and it does that now, with no blown speakers. I think I can save it by putting in some bracing.

 

[Kitsapbass]

There shouldn't really be more than like 12 screws, if you have a cordless drill shouldn't take more than like 3 minutes...but that's what I'd do.