Is it permissible to receive financial benefit in exchange for non-Islamic bank checks that a person used to obtain deferred goods, in order to pay off debts owed by the questioner?

It is impermissible to take a fee for a guarantee (e.g., pawning checks to guarantee a friend's merchandise) because it amounts to a loan that yields a benefit, and jurists have stipulated that making a charge for a guarantee is not permissible.