If Lisa only had three or four faces, interacting with her might be informative, but it wouldn't be engaging. We need to differentiate a delighted face with one that is merely very pleased. To express very pleased Lisa needs the great big smile, but we limit the exposure to teeth alone. As the creator of eGain Assistant, Rearick understands how to split hairs. I can tell I'm not doing very well.
Some companies have imaginary customer service reps.
Some companies use real CSR's. You might even want to chooses a cartoon character. Either way, Rearick has enough experience at this to have a few suggestions. Photographic portraits should be frontal facing only. Cartoon renderings should be three-quarter or frontal facing.