It's inevitable that you'll encounter angry customers who resent telemarketing calls. Explain your philosophy of handling such calls, and if you can, provide a specific instance that you handled well. For example:

I know customers are not always in the mood to receive a call. I find that apologizing often calms customers down. I always try to set up a callback time, because I don't want the customer to miss out on the valuable product or service I am offering them.