I stayed here for a quick weekend getaway. I didn't get a chance to meet Nicole because she was working when I checked in but I met her husband Kurt. He was extremely nice and gave me a tour of the space and showed me how everything worked. He was also nice enough to drop me off in Downtown Ballard so I didn't have to walk or search for parking on a Friday night. Though I didn't meet Nicole, she was readily available if I needed anything and responded promptly if I had any questions.
Regarding the apartment, it was decorated nicely. Very comfortable space. And they tried to think of anything you could possibly need there. I forgot my toothbrush and there was one in the medicine cabinet along with various other items that you might need. There were also snacks in the kitchen-bagels, fruit, coffee, tea..etc. I've gotten to airbnb's before late at night starving so this is a very thoughtful touch. As others have said you do hear footsteps from above but with it being a basement apartments that's the be expected. (Though I didn't need them they do provide ear plugs..It was always quiet at night).
You're 10 blocks from a bunch of shops, bars, and restaurants in Ballard so it's very convenient. I would recommend a car if you're planning on venturing out to other parts of the city.
Overall, Kurt and Nicole are great hosts and definitely recommend their place.