If You play in a punk or heavy rock band and the happy couple like that,fine,but you have to make certain sacrifices to keep all the guests happy.
I've played at a few weddings,and we have always told those who book us that we play what we play but are willing to take on board suggestions/requests if the are given in good time.
As we play some ska,Stax-Volt RnB,disco and old school rock we seem to cover all bases,but do'nt be afraid to try or suggest something different.
So far we have been well recieved,but remember that you will never please all the guests all of the time.
Ask the happy couple what they want you to wear.You may all have to scour the charity shops for cheap suits to sweat in!
Tell them that as a band you ca'nt play quieter than the drummer!
We had two complaints at a soundcheck for a wedding by local residents,so always be diplomatic too.
If you enjoy the songs you play it will show,and make the wedding guests happier too.