I feel your pain! We sent out Save the Dates a year in advance letting people know our wedding would be destination and details would follow. We searched high and low for the best rates for our guests and sent out our invites and then after our invites went out it seemed like no one cared to book! It was SO frustrating! When is your wedding?
If you went with a travel agent he way your "contract" is with the travel provider will depend on how long your prices are locked in, we didnt have a contract but FI and I had to place deposits for ourselves and then 30 trips were held at our rates for people to put deposits down within 90 days, after the 90 days prices were not guaranteed and could have gone up, maybe thats what your agent is talking about. For us $200 deposits were due by May 1st and the remaining amount due at the end of September. We had some people, including FI's mom who put down deposits within 30 minutes of the deadline. We weren't sure what was stopping people from booking either, it was the weirdest thing!