i donk know how a garage can get away with slapping over sills on in this day and age- imagine how many other minis they have done...
good outcome though, they should be willing to re-do it right and shows some good-will.
It's like I suggested earlier in this thread, It's surprising how many places/people either don't know the difference between them, the pitfalls of coversills or believe that they are better/stronger.
Perhaps if they normally fit coversills to Mini's, they may now not after being brought up on it so that would be a good result for all involved in the future.
The fact that they have agreed to sort this out speaks volumes in my mind.