How many letters does the top answer for “one who sells books.” have?

The most common answer is bibliopole (10 letters).

Crossword clue: one who sells books.

2 answers found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

bibliopole 10 letters web-def

a dealer in secondhand books (especially rare or curious books)

bookseller 10 letters web-def

the proprietor of a bookstore

one who sells. chaucer. 50% similar → seller