In any job interview you go you got to present your self well. First impression is the best impression mind it. This is a Call center, BPO or a Tele marketing job. The job nature is to talking, attending customers call and answering them well with in a shortest possible time. The customer may be from your country or from other countries. There is going to be some difference in culture, language and even basic perception between you and your customer.
The company foresee all the things to handle a customer. So basically they will be looking for some one, who is fluent in English, good understanding of the situation, ability to grab knowledge and change accordingly, kindness, Patience and pleasing manners, enthusiasm and hard work.
As a potential candidate you got to focus on all this. In interview, you must listen carefully, don't ask them to repeat again. Because listing is an ability, which is important for this job. If you ask them to repeat again and again, they might think that you are a deaf and ultimately you will loose the job. Instead ask them politely to increase their volume.
Wish you good luck