Dodged a bullet...
By reading this thread - thanks.
We went there because they're reasonably local and had a long list of potential cars. The salesman wasn't too bad, but even though I made it very clear we weren't going to put any money down on the day he tried is best to convince us anyway - that may be their tactics, but having done sales in the past I would certainly have gone a different route. You don't win by annoying the customer from the start.
Given that they almost only sell BMWs (in the Addington site at least) I was also surprised the salesman got his numbers wrong - surely he should know headline figures for the cars (500+ hp M3)? Maybe that's just me.
Having had some time to digest the experience I am surprised about the state of the cars on the lot - many of them was in quite poor nick for being 08-09 cars with deep scratches in the paint, rusty stone chips and tired interiors.
Having done a bit more research they're not even that cheap. Although I would be willing to pay a (small) premium if the car warranted it, nothing of what we were shown lived up to that.
So really - thanks!