It is about excellence in customer service, not whether you buy from an AD or grey market dealer.
I also had a terrible experience at an IWC AD in Zurich. When changing a strap they badly scratched one of the lugs and when I complained they said that I had already brought the watch in this condition and were accusing me of wanting to extract a free repair from them for a damage that I had done. They also told me that I was coming with a second-hand watch into their shop, even though I was the first owner and the watch still had more than one year of warranty left. Luckily, at the IWC HQ in Schaffhausen they believed my story and repaired the watch directly there free of charge.
On the other hand, I have had an excellent experience with a grey market dealer. When I traveled from Zurich to Basel to buy a watch from one such dealer, they offered me to pick me up by car from the train station to get me to their shop. In the shop itself, the grey market dealer took time to explain to me how the grey market works.
The bottom line here is: it is not about whether the seller is an AD or not, it is about commitment to excellence in customer service.