There are already articles out there in cyber space on how to run a mystery weekend for Bed and Breakfast establishments.
I won't repeat those steps just for the sake of search engine optimization.
You already know those are out there.
Instead I will add to those steps to help you run a mystery weekend that is not just average, but a darn near perfect experience for you and your guests.

1. Assign characters on a first come, first serve basis upon arrival.
   This way, you will be sure that key characters are assigned to someone who actually showed up and if there are any "no shows", the show can still go on without the extra players.
   
2. Require a deposit up front at the time of reservation.
   This will minimize the chance of a "no show" for your weekend event.
   Make this deposit non refundable after a certain amount of time.
   
3. The most important thing to do is to make an investment in your business and buy a murder Mystery game that is specifically written for Bed and Breakfast mystery weekends.
   Look for games that are written with the Bed and Breakfast in mind and actually take place over a weekend.
   Instead of buying a generic boxed game made for home dinner parties and trying to stretch it out over a weekend, you can get something made especially for your type of business with an itinerary for the entire weekend.
   After all, you wouldn't want your mystery weekend to feature a boxed game that one of your guests has attended before at a friend's house party or purchased and hosted himself for his own dinner party would you?
4. Another way to make this weekend memorable for your guests is to offer them a prize that they will actually like.
   Award certificates are fine, but why not give the winner something you know he or she will enjoy like a home version of a murder mystery they can play at home? If your guests are at a mystery weekend event, then the chances of them liking a grand prize of a mystery game are pretty good.
   Put those boxed games to good use and give them to someone who will play it at their home over the course of a meal.
   There is actually a program that will allow Bed and breakfast establishments to receive these boxed games for free for the purpose of giving them to guests as prizes.
   
5. Pictures! Take pictures of your event during game play.
   It doesn't have to be anything fancy.
   When your guest check out, give them a set of pictures to remember the event by (which will in turn help them remember their stay with you).
   They will look at them on their way home and show them off long after the event is over.
   

The above tips are sure to help you enhance the experience of your guests and help you all have a perfect Murder Mystery Weekend.