Simple. Don't do it. Your desire/need for income should never override your judgement or the best interests of others. A wedding is, for most people, the most wonderful day in their lives; perhaps next only to the birth of a child. It is also, for this couple, a one-time only event! If you screw it up it's gone forever. They deserve a true professional. If you want to be a wedding photographer it would be wonderful for you to apprentice with a professional for a year or two. Trying to become a wedding photographer on a real wedding would be wrong no matter how nice your photos. Wedding photography is a whole lot more than being able to capture nice photographs. Good luck.