I remember asking our cater what he charged for plate for the meal we had selected and was surprised how low his price was.  When I asked him what he charged for gratuity he responded the price is the price and gratuities are tacky and that no one deserves a tip.  IIRC we tipped him close to 25% when it was all said and done.  At the reception was when we realized we had not arranged to have someone scoop ice cream, he had his kids that worked for him serve the ice cream.