When hiring any vendor for your wedding -- photographer, musicians, caterer, location, florist, etc. -- it's very important that you have a contract and that you read it carefully before signing on the dotted line.
You want to make sure that your wedding date and time are listed, as well as the services they are supplying and how much you are paying for them. You also want to read over the cancellation and refund policy.
Each contract should also state what should happen if you or the vendor cancels. You need to know if your deposit is refundable or if you're entitled to other monetary damages. If an emergency comes up, will the vendor find a suitable backup or replacement vendor to cover your wedding.
And what happens if you cancel? Is there a cancellation fee and how much is it?
Don't be afraid to ask the vendor questions about the contract, and have your parents or your groom's parents read it too. They may have more experience than you and your groom do, and may have questions neither of you might think to ask.