The large bearing in my Alternator went out last year. The Alternator had a sticker on it showing it was previously rebuilt by Bosch North America; the bad bearing was madi in China.
I replaced it with an Ebay bought Chinese bearing for $2.50+ shipping which was not too much as the Ebay seller was local.
They wanted over $20 for an US made bearing and I felt it was not a super critical part and replacing it is not such a bad job.
I think China Bearings OK on the Front Hub; but, since the Rear Wheel Bearings are very labor and special tool intensive that might be the place to make sure you use high quailty bearings.
The ever haunting problem of risk verses cost.
Someone could "Ask Phil" to make sure they get USA/German bearings.
someone could join the Mercedes Benz Club of America and hope the Dealer gives a good discount to members (last year there was a thread on this).