An iar has opened an account for a new customer. the customer is "on the road" for 3-4 weeks per month and has given the iar verbal authorization to trade her account on a discretionary basis. the iar sends the customer a written power of attorney for signature and return. 1 week after opening the account, the iar hears of a good investment opportunity and buys 500 shares of the xyz stock at $50 for the customer's account. 3 weeks later, the stock declines and the iar sells the stock at $30 per share. the customer never returned the signed power of attorney. liability for the loss rests with the: