If that were true it would apply to most salesmen for prestige marques (and other luxury goods for that matter), not just MBs. Those customers are the salesmen's bread and butter - it's in their interests to treat them (us) well.
When most of their customers turn up in grubby shellsuits and with their mrs dripping with argos jewelry and fake burberry? They'll still sit them down and get them maced up on that '63 they've always dreamed of.
The days of Mercedes only being for the rich are long over.