My local dealer has a policy where they don’t give out loaners to customers who didn’t purchase the vehicle from them. After some hassling them the service manager essentially said that they work the price of the loaner fleet into their car sales price so you ‘pay for the privilege of the loaner’. They do have a shuttle van that’ll drop you off and pick you up pretty much anywhere but riding the dealership bus is kind of annoying haha.
Next closet dealer has sent me across the street to a chain car rental place on their dime and also given a loaner for a couple days (CLA 250).
Each dealer is privately owned and MBUSA says it’s up to the discretion of the dealer for a loaner, I don’t think they really get in the middle of loaner complaints if it gets brought that far.
Some decent advice is to try and find a trusted local independent shop that specializes in European and higher end cars and use them for routine maintenance versus paying mercedes dealer prices for their service ‘A & B’ plan and save the dealer visits for warranty work (if applicable). For example I can get my oil changed at the local high end euro shop for 65% of what the dealer charges, and they have customer service above and beyond what the dealer does. Your service A isn’t going to be much more than just that, an oil change and a glorified multi point inspection, but the reputable independent shop is going to do a courtesy multi point anyway with an oil change. Maybe go to the dealer once a year if you care about software updates but there’s a reason the service departments get called ‘stealerships’.