Be sure to send the referring person a thank you note or even a small gift for the lead. You can take this a step further by asking your customers to make a call for you or even write a letter on their stationery to their contacts, recommending your company. This is a more active referral system that can bring you significant results. I was taught this technique many years ago and it has gotten me through to levels in companies that would astound you. It's really simple.
People like to help each other.
It's human nature. If you cold call a business, especially a large company, and ask the person who answers the telephone if they can help you, they will generally go out of their way to be of assistance. Receptionists in particular can be extremely helpful. If you tell them what you need, they generally know who in that organization you should be speaking with. In larger companies, getting to the right person is half the challenge.