volving charge account means an arrangement between a seller and a buyer pursuant to which (1) the seller may permit the buyer to purchase from the seller or an affiliate goods or services on credit, (2) the debts arising from purchases, credit service charges and other service charges will be debited to an account, (3) a credit service charge may be computed from time to time on the basis of the balances of the buyer’s account, and (4) the buyer will have the privilege of paying the balances in installments.