On the crabbing problem the dealer reckoned with the latest tire spec on the AMG all would be good! at least he was aware of the problem.
I said, if not come winter I shall be banging on your door .
Get the dealer to put it in writing stating 'with the latest tire spec on the AMG all would be good' and eliminates the Crabbing fault. Because, and this sounds harsh - your dealer is 100% lying in order to close the sale
As Phil has said, MB cannot supply the required tyres for C43 & C63 variants, which, even if they could, only masks the fault. And the newly engineered Steering Knuckle components, which appear to fix the issue, have not been made ( yet ) for the C43 & C63 - so your car will not have these parts fitted.
You should also send them a letter + email confirming this position prior to taking delivery. This information will be invaluable when the weather changes and MB have your money!
In fact 2 years a go MB UK issued a statement telling their Dealers and Sales people to ensure they inform all prospective GLC customers about the Crabbing, stating it is simply a comfort issue and a characteristic of the GLC. This has subsequently been ignored by dealers because the sales people know customers are unlikely to buy a faulty new car.
Believe me, many of us have been banging every door linked to MB UK and MB Germany HQ for 3 years, as well as using the media / auto magazines and forums etc. They are pretty good at ignoring customers complaints - MB must run a special Training course
Enjoy the car