Polite and professional.
I personally have no interest in models or trains but the whistle stop is the first place I go when I need small parts in the area. They are very knowlegable (there are usually about three people behind the counter waiting to help you too) and I have better luck finding what I need than at the hardware store. I especially appreciate their real commitment to customer service, which is sadly rare these days.
Lionel, You've Got Company.
Sure this shop helps out the parents assembling a toy under the tree on Christmas morning. But it doesn't cater to them. These folks are serious about the railroad. The book section alone is bigger than the poetry section in most large chain book stores. And they can lay their hands on any volume. The front rooms are crammed with model trains, landscaping detail, balsa wood for the do-it-yourself perfectionists, videos, magazines, and "railroadiana" of all kinds: signs (big ones), lanterns, collectibles, and hats.