My parents and I were planning on booking rooms for the night before the wedding at a Hilton which is near my venue, where my fiance and I will be staying after the wedding. When my mother called Hilton they said they were booked because of conventions going on that weekend, even when she tried to beg and plead with the clerk. At first it was looking like yet another disaster. But when she started looking around on the travel web sites like Orbitz, Travelocity, and etc., she was able to get a room on Booking.com. Apparently the sites take blocks of rooms that you will then have to book through the site. Especially with plane tickets we usually try to avoid those sites and just use them to compare prices before booking directly and avoiding the convenience fee charged by the site. But in this case, it would have caused some logistical confusion for my parents to stay at another hotel because my fiance and I were planning to leave some items with them before we check into our room and after we check out. So I was glad just that they were able to get a room!
Just wanted to spread a word to the wise for you and your guests to keep trying different travel sites even if the hotel says they're booked!
Whoever said it was supposed to be happily ever after is a big fat liar.