Believe joker to be a bit of plastic? (6,4)

I believe the answer is:

credit card

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

'a bit of plastic?' is the definition.
'credit card' can be an answer for 'plastic?' (I've seen this before). I am unsure of the 'a bit of' bit.

'believe joker' is the wordplay.
'believe' becomes 'credit' (I've seen this before).
'joker' becomes 'card' (joker is a type of playing card).
'credit'+'card'='CREDIT CARD'

'to be' acts as a link.

Can you help me to learn more?

(Other definitions for credit card that I've seen before include "Entrant to 1 Across [CASH DISPENSER]" , "Piece of "plastic''" , "Means of borrowing" .)

I've seen this clue in the Sydney Morning Herald.

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