promoting is the key to earn from facebook , you can promote your site/ blog easily and thats the key to increase your sales or anything , but i think oyu cant use facebook directly to earn..
Not sure about Fan pages but yeah you can earn a huge amount of money by creating Facebook apps. Some famous Developers earn a lot of money. make a application(interesting one) and manage to get users in ten thousands after that you an earn a lot from Advertisements.
this a good point for the author....but you can look forward for fan page also..it will help you to sell product (if you have).....thank you once again(i am at hurry ,so short answer).