How disappointing is it not to be able to hear the wedding ceremony? I have received a lot of praise for having a fantastic public address system and high quality microphone. It can make all the difference to a ceremony - people love to hear what is being said!
It is a legal requirement (according to The Celebrants Code of Practice) that all registered celebrants ensure the ceremony be audible to all of the guests. Make certain that your celebrant has a high quality and, if necessary, portable (not requiring mains power) public address system. Make sure they can still use it if it's windy if you are going to be on the beach and how they protect against surplus noise across the microphone.
Ask if they have cord free hand held microphone for the delivery of readings, poems, etc. Do they have the facility to play your music through their system: cd's, iPod's, computers, connections?