I finally took the plunge and bought a 2017 C63 (non-S). Purchased out of state, and did a pre-purchase inspection at the local MB dealership. Everything checked out fine. However, when I went for the dreaded Maryland Safety Inspection at a random, local shop, they failed it for a number of odd reasons (for example, they say I need new rear rotors at 20k miles, but the brake pads are fine??) Does anyone have a local recommendation where I can get some assistance passing the MD Safety Inspection without paying for unnecessary "repairs"?

I have no experience with this. Is there a local MB dealer that performs these inspections?

I don’t believe MB dealerships (or any of that kind) can perform the inspections. Typically just auto repair shops and gas stations with the yellow MD inspection sign out front can do them.

Have you called the MB dealership where you bought the car and talked with them? If they did a PPI, they should have either caught this, or they can give you some guidance. I took my Porsche, which I bought out of state (CA) to a local place in PG County to have it inspected. No issues, but in my case, the car was under warranty, and I would have been able to take it to Porsche to have them fix it for free for an item like yours.

You may need rotors as the old owner may have just opted to put new brake pads on as it is much cheaper and he/she didn't want to invest in a car they knew they were trading it in soon. I replaced pads and rotors on my Audi S7 before I traded it in. I hated to do it, but my pads we low and the sensor was on, so it was necessary. Maybe your owners just did the least expensive thing they could do to get it ready for sale.