boston is my local store and i honestly find their SA's to be more pleasant than ones that I have seen in other stores. as for cultivating a relationship, i got a call about my first birkin the same night that i went in the store for the first time and bought a bracelet and a scarf (VERY good stroke of luck!).
after that, i have been purchasing small things here and there, always with the same SA, with whom i have a great relationship. she calls me a lot when things come in that she thinks would interest me, and i make a point of going in to visit at least once in awhile even when i'm busy. she actually just took my order for podium this past july, so i should be getting my second birkin next year sometime hoepfully.
i think it helps to show a lot of interest in their products, ask questions, stop in every so often. the store is on the smaller side compared with the huge ones so they may not get quite as much inventory as other stores, so it may be harder to be able to place special orders and such. hope that helped!