ignorant, innocent, foolish, simple, immature

ignorance, foolishness, infatuation, stupidity, folly, idiotism

a wise foe is better than a foolish friend

unintentional, unwittingly, by mistake, undeliberate, inadvertent

ignorance, unwittingness

one avoiding the payment of his/her dues or debts

miser, not liberal, non-payer, evasive, defalcation,

non-payment, state of not paying what is due, non-payment, evasion