Tell me how you developed your largest existing account.

"With my larger accounts, the success has all come down to building relationships through offering kindness, and genuine care and support. Excellent customer service skills and a personalized touch help, as well. I am sure to remember their kids' names, birthdays, and congratulate them on company milestones."

The interviewer is looking to learn how you took a modest account and grew it into something sizable. Typically, the most significant opportunity lies in an existing account rather than new sales as far as ROI goes, so it's essential that you're able to sign a new client, get their business, and continue to extract more business from them. Share a success story about how you've done this in the past.

"In my current position I developed my largest existing account by visiting their office on a regular basis. Showing that I was keen, and prepared to service their company with a great sense of attention, was what they wanted to hear. The company went from spending just 30K per year with our company, to nearly 100K in just six months. I continue to grow this account by being consistent and always delivering faster and better than they expect."