"Καλοδιάβαστο" is a wish to someone who just acquired a book to enjoy it. It's usually said when a book is gifted. I wouldn't be surprised if a small bookstore owner would say this to a buyer, after a nice conversation about the book (a store clerk, not so much, I believe).
"Well-read" would be translated as "καλοδιαβασμένο". "Kαλοδιαβασμένος" can also be used for people who are well-educated on a certain subject or generally.
"Well-read" would be translated as "καλοδιαβασμένο". "Kαλοδιαβασμένος" can also be used for people who are well-educated on a certain subject or generally.