Well, I went up and bought it on Wednesday. An honest-ish dealer, I'd say; the car is nice, but there were a couple of minor surprises.
The NTG2.0 COMAND unit in the car is completely dead, and the dealer didn't seem exactly astonished; no doubt coincidentally, the boot panel that gives access to the relevant fuse block had been disturbed recently... Hmmmm no.1. (Not a problem; I'm putting in an NTG2.5 anyway)
Oddly, the car was fully warmed up, and had actually been run for twenty minutes, but covering 0 miles, before I arrived. I did rather wonder why; Hmmmm no. 2. No funny noises, though, so I thought I'd take a chance.
(I now know why; to charge the battery. The dealer did say, out of the blue, that it had a new battery, but there's no evidence of that, and I rather doubted it; 12.5 volts overnight after a 200-mile run suggested it's a little tired at least. I put it on the Ctek, which did its stuff in less than two hours, though, so I guess it's OK).
Bloody boring, trundling down the motorway with no music or radio, but I could at least hear any funny noises. There were none. Reason to be cheerful no 1.
Good tyres, matching Michelin Latitude 3 all round, nearly new on the front, and nearly new discs all round too. Not a sign of a car run on the cheap; reason to be cheerful no. 2
It drives pretty well; ample power, no feeling that it's lacking in torque in the lower rev range (maybe I should try harder...), revs cleanly to the red line (not that there's much need for that; again, maybe I should try harder...), doesn't roll too much, corners OK once the roll has been established. Doesn't sound nearly as nice as the CLS for my taste, but it's OK. Reason to be cheerful no. 3.
Fuel consumption? Well, averaging 68 mph over 207 (nearly all motorway) miles gave 21.0 mpg. Reason to be (relatively...) cheerful no.4.
Overall, I think I was right; it's a good 'un. Result.