We found the place we want to stay in Cinque Terre by reading Rick Steves' book. However, when we emailed them (two times) to see if they have a room available, they have not responded. Should we assume they have no availability?
Yes.
I've also been looking at Cinque Terre for places to stay in September using RS book. I went directly to the hotels' web sights and submitted a reservation request and HAVE received emails back. Of the 5 places I've checked, there's only one that has not responded. Unfortunately for me all but one were fully booked.