In our experience with call centers, I have learned the hard way that you should be cautious, very cautious when choosing one. Here are some things we have learned over the years:
1) Place a lot of test orders. Your business reputation is on the line with agents that probably could not care less. You had better check up on them a lot. When you call and place test orders, you will be amazed by some call center agents–amazed that anyone can be that stupid. Just remember that those people are reflecting on your brand.
2) Watch that contract. I remember when we had a call center handling calls for us when we were running national radio ads. We were spending big money on those ads. One day, we did not get our order batch. We found out that the call center had been down for 24 hours without even notifying us! Do you think we were ever reimbursed for the tens of thousands spent on advertising while they were down? Make sure you have this issue and similar issues covered in your contract.
3) Visit before you hire. I remember a time when I visited a call center we were using. Walking into that dump was very enlightening and helped me understand very quickly why they were doing a lousy job. Make the visit first and see the professionalism (or lack thereof) for yourself.
4) Train the agents. Visit occasionally and spend time with the agents. Give them free products and tell them how to sell your products. They will appreciate it. By the way, you can explore incentivizing the agents as well. I assure you that no call center will stand in your way.
In general, call centers are a necessary part of growing for most internet retailers. The key is simply this–you cannot hire one and forget about them. You have to remember that those people whom you have little control over have the ability to make or break your business. That is scary thought.