Once you know who your prospects are and where their pain is, you must be able to explain how what you offer directly addresses that pain. Of course, you probably will have to do the standard ROI analysis just to check the financial box, but it's the fears that aren't realized and the costs that aren't incurred that may be the most valuable to your prospect.
But, it's not enough to communicate your value to get the initial sale. You have to keep it up, constantly uncovering new pain that may have developed and continually reminding all your stakeholders how you are fulfilling their needs. It's a strange—but—true phenomenon that some people do such a good job so quietly that they make it look easy. I know at least one test manager whose company thought the software was stable, so they slashed her process team—only to eventually discover that her process team was the reason it was stable.
Again, remember to communicate in your customer's terms. Don't bore everyone with your S-curves, test case inventories, and defect rates. Those metrics are important to you and your team but not necessarily to others. Instead, couch your value in terms near and dear to your customer's heart. For example, the car manufacturing test manager reported each week how many production processes were verified and, if any issues were uncovered, how many incidents were avoided and their potential cost. Instead of saying, "We found a Sev 1 defect due to database corruption," he said, "We prevented a failure in the electronics assembly process that saved $60 million in lost production." Both were true, but the latter spoke to his audience.
And, please forget all those stereotypes and clichés about the pushy and relentless salesperson. As a friend once noted of the Amway empire: Sooner or later, someone has to sell some soap. Just because you test software doesn't mean you don't have to sell.