^^^I've had this happen to me a number of times. The worst was with the Tstat; I have the early/116 PN, but the system subbed in a late/119PN part. I realized when I got home, so I called and SFBenz ordered the correct part (that parts not really on them). The issue came up when they tried to charge me a 20% restocking fee on the part they incorrectly ordered. I pushed back and they agreed to waive, but just the gall to even try this got under my skin. I doubt they make much if any money on us doing this, but they nonetheless are representing the brand and the company, and I like to think they ought to be willing to put in a some extra effort to support enthusiast owners like ourselves and keep the cars on the road.
@Jlaa I think I overstated it a bit, she's always very personable and nice, and generally things have been fine, but along with the above case I've had small gaskets/orings be missing in an order when I double check at the counter. To their credit she's usually been able to find it in the back. I do feel fortunate that their is a local Benz dealer that I can order parts to and pick up for free, so maybe I shouldn't complain.