My dealer is finding out from the factory what will be fitted to the car when I order. Obviously this may change but they can tell me the current tyres, they are genuinely sympathetic to the situation and seem like they want to find out, there has been no BS from them so far.
Last night I flew into Southampton Airport and Merc is just on the perimeter so I had a look round their car park. Two C class C43's there ,one on 18's with Bridgestone Potenza's fitted (which I understand don't suffer crabbing) and a pre reg car (below) that was for sale on 19's which had the Continental SSR's (which also don't suffer as I understand). These were both new cars.
Used Mercedes-Benz C-Class | Marshall Mercedes-Benz
I know we cant assume anything but it does look like the non crabbing tyres are now being fitted by the factory, which gives me some piece of mind I think to go ahead, as does RL-C43 Coupe above with his Firestones.