I've been a member of PBS for some time now and this is the first time this has happened to me. I had a book requested from me but it was in storage in a box. When I got it out, it had stains on it so I declined to send that one book. Does anything happen to my account because of this?  

You should be fine, it was a single instance of declining a book and we all know things like that can happen to books that have been stored, especially if they're out of sight. It's much better to decline than try to send out an unpostable, that does get PBS's attention faster. The order just goes to the next copy posted. If you were to make a habit of declining orders your account might be flagged, though. Maybe sort through your books now and then and pull listings on any unpostables.