I've bought my last 3 cars interstate including the M3 and a Porsche 911 Turbo none of which I got to test drive before buying but I did get all cars thoroughly checked before hand by experts who knew the cars inside and out (BMW & Porsche etc).
The Porsche I didn't drive until it arrived in Brissy from WA .. As for the SMG I had a great rapport with the seller and it only had 48k on the clock, that along with BMW's stamp of approval sealed the deal ..
I'm still getting used to the SMG as it's only been a week but so far I love it ! I've always been a manual car guy so this car is something new, I've gone for the clutch pedal a few times only to find it GONE !
I did the reset trick too and found that smoothed out the change heaps ... So my 2c would be JUST DO IT !