When you would like to be very polite, such as in business. When you would like to be really nice to your customers, use さま. Most of the time, さん is polite enough and さま is too polite in daily conversations. さま appears more frequently in written Japanese. When we write a letter to friends, the name next to his/her address is accompanied with さま.

Please see this wikipedia to get a better understanding of it. http://en.wikipedia.org/wiki/Japanese_honorifics Hope this helps.