Since you are now in DC, there are 2 B&M camera stores I can recommend:
District Camera (formerly Photo Craft) -
districtcamera.com
This is my first choice when buying new photographic equipment. They moved to a new web platform not too long ago, so not all they sell shows up when browsing, but it should show up when you search for an item they sell. They do not have as broad a selection as the big stores, but are willing to try to order things if you ask. I don't think I ever bought filters from them, but I have bought quite a lot of new stuff from them over the last 10 years, including all my Z cameras and lenses. They have a store in DC. I am only familiar with their Burke store, where I go to buy stuff (in person, never online).
Ace Photo -
acephoto.net
This is my second choice for buying new photographic equipment, when I cannot find it at District Camera. I am familiar with their Ashburn store (not far from the Dulles airport). This is where I bought my Df (when even the Nikon warehouse was out, they had a couple in stock), and my CFExpress card/reader (they got their first shipment much faster than District Camera), among other things - again in person, not over the internet. Their Ashburn store is large enough that you can wander around looking at stuff, which is why I prefer to go in person. I bought a few Nikon CP filters from this store - the price was higher than from B&H - but I got to check them before buying, and they were new.
B&H would only be my third option, for stuff that I cannot find at these 2 stores.
I can't say anything about buying/selling used equipemnt at these stores.