Crossword Genius

To buy it, must one be in credit? (3)

Ross

I believe the answer is:

car

I'm a little stuck... Click here to teach me more about this clue!

'to buy it must' is the definition.
I can't judge whether this definition defines the answer.

'one be in credit?' is the wordplay.
'one' becomes 'a' (a thing is one thing).
'be in' indicates putting letters inside.
'credit?' becomes 'cr' (abbreviation).
'a' placed inside 'cr' is 'CAR'.

Can you help me to learn more?

(Other definitions for car that I've seen before include "Railway carriage; vehicle" , "Road vehicle; rail coach" , "Wheeled vehicle" , "Private vehicle" , "Private transport" .)

I've seen this clue in the Evening Standard.
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