I dunno what it's like in your neck of the woods but around here most detailing workshops concentrate on volume cleaning major manufacturer's models for dealerships with little or no experience in prestige/concourse paint finishing.
Try a prestige panel shop. They won't be too expensive but more importantly will know what they're doing. I've worked in both and can testify.
At any rate, a light fine-grade sanding and proper buffing/finishing (detailers generally do the buffing but not the buff-finishing, so leave all the cutters swirls and ultra-fine scratches in the paint and just polish over the top...you can see it out in the sun on various angles as psychodelic swirls instead of a deep, liquid finish).
Especially since your car is black, I suggest a high quality prestige paint shop/panel beater. And get the whole thing buffed/finished whilst you're there.
Even road dust scratches black over time.
And since you're paying for a professional job, be a real hard arse. Tell them how you don't like seeing any scratches in the paint at all and then show them when you move your head around different angles in the light you can always see scratches, it's so annoying. Paint should be liquid smooth and deep. Pay them extra. Offer to take the guy's wife out for dinner. But no scratches when you pick the Merc up.
That should get you a proper finish all over. Make sure it's a top notch prestige paint shop though, who're used to dealing with pedantic owners in an honest fashion.
Oh and you don't like touch-ups because they look messy. Make a couple of complaints about the C230's styling too. Like the headlights could've been a little squarer 'round the edges and the steering wheel a little further over to one side. Be nice, just eccentric.
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