The most common and most likely answer to this crossword clue is the 6 letter word CARDED
I've seen this crossword clue in The Times
C
A
R
D
E
D
Buddy explains!
The straight part
We know that "booked" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case booked = carded.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does CARDED mean?
CARDED verb- To check IDs, especially against a minimum age requirement.
- To play cards.
- To make (a stated score), as recorded on a scoring card.
- To use a carding device to disentangle the fibres of wool prior to spinning.
- To scrape or tear someone’s flesh using a metal comb, as a form of torture.
- To comb with a card; to cleanse or disentangle by carding.
- To clean or clear, as if by using a card.
- To mix or mingle, as with an inferior or weaker article.