2) Have a relatively limited selection
3) Not very well organized
Here's why I'm jaded - I lived in Eureka, Calif. for a year. Eureka has great used book stores that have enormous selections and ridiculously cheap prices. And, furthermore, Eureka is in the middle of nowhere - stuck behind the redwood curtain, 300 miles north of San Francisco and 5 hours (on a good day with no rock slides, major fog or rain storms and so, if you're familiar with the area, basically the planets have to align) from a major city with a population of 18, 000 people. So, to continue with my long rant, I would expect the capital city of my nation to have a semi-comparable used book scene....
What I found at Second Story Books was a disappointing, semi-organized, second-rate used bookstore. I went in hoping to find a treasure trove of political books, biographies and history books, but I was sadly mistaken. Additionally, their paperbacks were priced at half the cover price...leaving most overpriced, at best.
You might find what you're looking for at Second Story Books. They have a semi-decent selection of vinyl, and the table outside was all marked at $4 a book or 6/$20. If your expectations are low from the onset then you might leave happy. I, as usual, went in with high expectations and left empty-handed and unfulfilled.