My 2000 mercedes c230 shakes when get up past 50 mph. What could be some possible problems?

If it is not in the suspension, have them check the motor mounts. Depends on the miles you have on the car. A faulty motor mount can cause a shake and imbalance in the engine which will show up at higher speeds. Like others have said a balljoint or tie-rod could cause it as well. Ck the mounts if all other variables ck out good.

If the tyres are properly balanced the next most common problem would be an out of round tyre. Most tyre shops can easily check for this, usually with out charge. You could move the front tyres to the back and the back tyres to the front and see if that makes any difference. If not, look for universal joint or drive line problems.

It could be a few different things such as a bad strut or shock,a bad ball joint or tie rod get these things checked out because if it's a ball joint or tie rod it could be potentially dangerous.

If your car shakes, it's most likely that your axles have gone bad. Have it checked out by a mechanic.

Its also possible, if you hit some real bad potholes, or a curb or something, you may have bent a rim

Tires, either they are wearing out or out of balance. but certainly tires.