That really sucks, this is my biggest problem too that SAs can be so rude, sometimes even when you are planning to buy something but especially if you have a problem or just want something out of the ordinary. This should never be the case, especially not considering the company but sometimes other stores are different.
I am planning to open my own store in the next year or so as until now I have mainly worked with stones, dealing diamonds, and planning designs but I do know when that happens I will buy back, repair and in general want to offer people great service as jewelry is really not a cheap thing and people deserve the best service when they spend that much money and they should be allowed to change, sell back, etc.,though I do know it is not realistic to buy back at the same price but people should at least be allowed to pay a small percentage for an upgrade to a new version, anyhow the point is to work with people and try to make them happy IMHO. I know that means a lot to me.
I too visit other stores and vendors at professional shows and there are some that stand out. In Vienna where I now live Wempe gave me great customer service and I only brought in a piece I bought from a customer and wanted to have it checked, I was curious how old the piece was as it looked great but upon closer look I was sure it was older, they were amazing really, the service, the atmosphere, they offered to serve my pieces even other than Wempe and in general I was just treated great. That means a lot as if I was your normal customer that is the place where I would shop.