Re: ABOUT TO BUY USED
It's possible that is what it's from, a little bit of water and these pressboard panels SMB uses just get destroyed. But you're right, that is a lot of water damage.
The good news is that floor underneath the damaged panels is practically impervious to anything I've thrown at it, so you're looking at replacing the panels- not tough if you're good with a jigsaw or have a router. It's basically remove 16-20 philips screws, trace, cut and replace. You're not going to get the fancy edge SMB has on, but it will look better than rotten particle board. SMB could also replace, as they still use the same stuff every day- have no idea the cost, or if you want to bother.
If it's right in all the other ways... uh, where are the kids going to sleep?