I know that dealership, complete shower of cowboys. I know guys who own Mercs who take them far and wide to avoid this place. I know the car, nearly bought one myself at auction a few years ago, £168k seems a bits strong.
The only time something similar happened to me was in a friends Mazda RX8 when I thought I could do without the traction control/stability program and turned it off.
I soon discovered I was wrong as I traveled sideways down the road after a sharp right under power. Luckily i got it under control and no damage was done (except to my underpants).
You have to remember whatever the reason for this 'mishap' if you are in the mototrade driving/delivering/road testing day in day out the laws of average will dictate sooner or later something will happen ,if not on the road in the workshop...hes not the first and wont be the last seen it a few times.