At 106 W. 25th Street is the Kelmscott Book Shop, which is described in a used book hunter's guide as nearly perfect. I won't argue. The peculiar architecture gives it two second and two third floors, reached by different staircases. The stock is divided into categories, but often on fast guesses—the archeology section often has lost-race novels, for instance. I have found things here that bibliographies of the field (and even of the authors) omit.
Down the street at 24 W. 25th is the Tiber Bookshop, more ordinary but still very good. They have general hardcovers of the last 20 years and collectible paperbacks.
In the antique row along Howard Street is Drusilla's Books, specializing in old children's and illustrated books. For someone interested in books from before the Second World War (which is to say, the stuff in the Bleiler Checklist) the best bargains may actually be found not in bookstores but in antique shops. However, the people who run these shops are quirkly. A price request may be answered by "What do you think it's worth?", which can cause real problems with your conscience. If you hang around another couple weeks after the Worldcon, the Baltimore Convention Center has an Antique Show and Antiquarian Book Fair—but it will be expensive (at least the books).
The light rail system runs by the antique shops and has a stop at North Avenue. If you get off there, you can walk to 2104 Charles Street, the Baltimore Book Company. Good store, a little high-priced, but they know books.
BNN Books at 36 W. 25th has only donated books, and the donators see to be all hard-left political types. But something recent and of interest books may be there, and when you are at the above stores you are already in the neighborhood.
The Raven Bookstore at 1113 W. 36th does not have a large stock, bu I would have to say I have never left it empty-handed. It's a long walk from the light rail Woodberry stop. Call 410-889-7869 first; the hours have gotten undependable
Book Rendezvous at 805 Light Street (Light Street is St. Paul nort of Baltimore Street) has a good selection of 70's & up, some older, hardcove sf on the ground floor, so-so general fiction, and the basement is all paperbacks; 12 Murray Leinster titles on a recent visit. They are open 12 - 7 p.m., 7 days a week, and are fairly inexpensive.
The Book Miser at 906 Fell Street (just east of the foot of Broadway) is general books, on the expensive side. I would not think much of it, except that it has so many books—outside the field that I own.
T-11 Books 1705 Pratt is a few blocks north of the Book Miser. It is crowded, and over half paperback. The store occasionally has a $1 sale, or even $10 for a bag, on hardcovers in the outbuilding.
And finally, north of 32nd Street, at 3360 Greenmount Avenue, is White Hart Books—now under new management. You know them from conventions, but may not be aware that the second floor of the store is all used books_hardcover and paperback