Hello,
I have a C350 with 13000 miles, and needs Service A.
Need some advise on whether to take it to the dealer (charging $250)
or to a certified mechanic (http://memphisgermanautotech.com/) (charging $120)

I called mercedes and they are unable to verify that the mechanic is certified.
I am afraid that the warranty may be void if I take it to the certified mechanic.
Please advise!

 

Exactly right. You do NOT have to take your car to the dealer ever again if you don't want to. Your warranty will not be "voided" if you take it to another mechanic or an independent. All you need to do is keep records of when and what they did. That's all. As long as they did not do something improper to void the warranty of that particular issue, you are good. You can take it to anybody to change the oil, etc. Just keep your receipts.

For some reason, this belief started a long time ago and won't go away.