The owners manual & service book explain it further. depending on car model year, limits can be from 10K to 20K miles or 365 to 730 days between services. Important to note that there are brake fluid services that your service booklet demands at every two years- when at the dealer for this service and check dealer will go over oil service with you.
Mercedes has a booklet that specifies all the different oils you can use and at what ambient temps the oils work best in. call 1-800-MERCEDES (or your dealer) to order a copy.
Dealers are independent and can charge what ever they wish for labor and supplies - call and compare