Your wedding day will only happen once. The memories will last forever but, great pictures and videos will allow you to keep and share the memories in a special way. If you are planning to hire a professional photographer, it might be a good idea to have friends and family taking pictures as well. Every moment of your wedding day is only going to happen once and everyone will see it differently. Photographing your wedding is a fun way for friends that are not in the wedding party to feel they made a valuable contribution.
There might be guarantees from a professional photographer but, what good will those do after the ceremony? Those moments can never be captured again and if something goes wrong you will have no recourse but perhaps a financial refund. Ask others to take photographs and video also, you should have no problem enlisting back up photographers.