Basic servicing always done at main dealer, though they do know me and the car so are sympathetic and don't just go off what the computer tells them should be done. I also get a nice discount now as it's over three years old.
I'm the same I suppose, though my dealer love the car and have been encouraging throughout. They know exactly what it's had done to it and just do a bare minimum to it on servicing. This time it's due air filters, plugs and brake fluid though they won't touch any of these things as the plugs and fluid have been recently changed, and their filters won't fit my intake.
The service manager always likes to take it for a test drive though at least has the courtesy to ask me if I mind.
Smart ForFour AMG Black Series Night Edition Premium Plus 125 Powered by Brabus
Perhaps worth mentioning that it has been remapped and ask that they check with you before applying software updates. Otherwise, servicing a tuned AMG is pretty much the same as servicing a standard AMG, which is pretty much the same as servicing a Mercedes. The only difference is the AMG premium some dealers want to charge!
Mine was originally with Privilege, though they will only insure up to an increase in power of 21% for some reason. I think most of the mainstream companies tend to be the same.
I now have it on with A Plan who have been excellent and, with all mods declared, it still works out around the same price but I'm allowed a 25%+ increase in horsepower. Shopping around is essential though, as there are some very strange prices floating about...