This is a slippery slope. When 3nd floor is sealed and temperature is close to 72-76' all year. More sqare foot is used and costs can go up. I have seen one person go to 8 body's after building is sealed and new HVAC systems are put in. I put on paper 30% saving and cost went up 40% Cost per person looks good but cost per building went up 40%. DOE-EPA - AEEE - has a lot of studies on this
Not sure if this really answers the question, but this study (link below) looked at what actions people took following the audit to calculate savings.
Evaluation starts on page 293
Good question. I'm somewhat new to the game but I'd say if there isn't one, go directly to as many auditors as you can and see who will allow you to do an initial phone interview with recent customers.
ACEEE has done research on this topic. Look on their main website, but also in the Summer Study archives.