Possible Clues:

• Agreed about books I see can be bought without cash
• With an agreement to pay later
• Part of season ticket to be paid for at a later date
• Working, get correct mark, attaining credit
• By instalments, fine assumes trust, I see
• Proportion of season ticket still to be paid for
• Working, getting correct mark, attaining credit
• Allowed to purchase books (mid-range of prices) with payment deferred
• Time behind bars, maybe, following round to be paid for later
• Ill-educated type concealing books not yet paid for