Hi, aj, welcome to the forum.
You'll probably find lots more useful information if you post questions about your specific car in the forum for it, the W208 forum. Just scroll down the main page and you'll see it.
That said, 100,000 miles is kind of a benchmark. If things have not previously been timely done, that's plugs, all filters and fluids (including transmission), belts, hoses, perhaps shocks as well. 02 sensors are estimated for 100K but I'd simply wait until you get a trouble code, then replace them. The front suspension should have a thorough inspection as well as the motor mounts.
Other than that, keep driving it.
I agree with DB's comment, who is this "they" you're referring to? No competent MB wrench would tell you that, it means you're due for either an A or B service and when that is complete the service indicator is then reset. Thus if you're not competent to do the service, run away from this nebulous/nefarious "they" and get it to a good indie who can help you care properly for this car.
See you in the W208 forum...I hop in there occasionally as there are lots of commonalities with the W210.
Take care and enjoy the ride,