does the amg c43 2017-2018 model need to change the differential fluid at 2k miles?

No. It's not a limited-slip differential.

First of all this is not the forum for your car mate.
Second, since the car is pretty current somewhere in the books you got there is a Service Manual which will tell you what and when you need things done.
They spend a lot of money they include in the cost of the cars they sell to make these things so they are worth reading.
Sales people are notorious for telling owners to get service not required. I have been driving these cars since 1987 and they still try to pull this BS on me.
Read the manual and take all the guess work and opinion out of it would be my advice.

I didn't look but here is the 2017 C coupe service manual and the C43 AMG should show up in there.

https://www.mbusa.com/vcm/MB/Digital...ce_Booklet.pdf

Typically in the service intervals you just follow the ones denoted for c-class, if there is anything specific for your model, it will note it, like the 2k diff change, will say specifically which models or which differentials need it.

Hi Alex, In your lengthy MB experience have SA actually advised you on stuff that was not present in the maintenance booklets? Isn't that just outright lying?

I have seen this, not with Mercedes, but the Honda dealer told their customers to come get an oil change every 3500 miles like in the 80's but the book was 9k oil change intervals - just the dealer up selling service and saying the book is the absolute longest, but more is better they will claim!

guess I am a w205. Will post in proper forum ( newbie ). Lose the "first of all" start, that's used by DH's. anyway onward and upward. After learning how to read the insane (JMO) service guide I deduced that my C43 does not need a dif change.
thanks for the help.

Not a service advisor which I put down in part to the fact that I have been fortunate perhaps to have good ones. I had one at Burlington Motor Car (now Mercedes Benz Burlington in Ontario) and out here in BC I deal with the service manager most of the time but that said his SAs are good too.
What did happen is when I bought a new CLA45 AMG in 2015 the sales person said to me as I was getting in the car to leave to be sure and make an appointment to have the rear diff changed at 2000 km.
Well as one who pays attention I have never had a new Benz that needed a rear diff change in 2000 km.
I went home and read the manuals including the service manual so I could get a feel of how that car stacked up against my W212, W211s etc and no where did I see anything in the CLA45 AMG column about changing the rear diff at 2000 km. In fact as I recall that was a 4 yr item.
Just to play the devil I was talking to the service manager and asked him when the rear diff on that car was to be done. His reply was he wasn't sure of the mileage but he thought it was out at 3-4 yr. He pulled it up on his computer. Bingo. He was right.
This is but one of the reasons I do not get my cars serviced at this dealership which is 30 minutes from my front door. I drive 1.6 hr to get it serviced because those guys are trustworthy, honest, care about me not only as a buyer but an ongoing customer and we have fun. I have always made a point of getting to know the techs that work on my car and I can actually ask for a specific tech.
Your question however brings me to a pet peave and that is why do people who buy any Mercedes and particularly cars like ours that cost over $90K CDN not invest a bit of time even if they put them in the loo and read their manuals particularly the service manuals? An informed owner cannot be conned particularly if they are diligient in getting their cars serviced at the correct intervals.
How many times do we see questions about fitment of tires? All the recommended sizes are on page 349 of my manual. Online tire seller's tools do the rest.
This case is the same thing. Read the manuals.