To me, a book is too personal, in regards to what an individual might like to read.
Therefore, a bookstore Gift Voucher is the way I would go, even if I know the recipent's book 'tastes'. By a GV, you're giving also the 'gift of choice' & I think that's lovely.
When I left one place of employment, I received a bookstore GV worth $280......to me that was like winning the Lotto!
Everybody knew I enjoyed book reading, but my 'genres' were SO eclectic, nobody would have an idea of what I'd enjoy!
I doubt ANYONE would think of the title of just ONE of my favourite books.........
'The Effects Of Volcanic Ash On Aircraft'.......wonderful book, especially chapter by Captain Eric Moody, who got a BA 747 aircraft safely to Jakarta, after going through volcanic ash from Mt Gulaggung, on flight originally Kuala Lumpur-Perth!