Mercedes vehicles require the use of special tools to be properly aligned.
Mercedes has worked with one of the larger companies that make the alignment equipment that most shops use, but the equipment has been Modified specifically for Mercedes vehicles.
I would go only to the dealer or an independent that specializes in Mercedes cars as they are sure to have the right equipment.
Stevebfl has answered many questions on alignment issues.
Do a search under his username and you'll see what I mean.
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".