I'm not sure exactly what type of research you're doing to get exaggerated volumetric estimates, but I assume it's some sort of concept test methodology involving purchase intention ratings? If so, there is a large literature, mostly from the 1960s, about adjusting purchase intentions to counteract exaggeration. A good source to look into is the book Design and Marketing of New Products by Urban and Hauser. It's pretty much the bible of new product research and it has a whole topic summarizing the research on the estimation of market potential.
We also often see overstatement of demand with conjoint models, so I don't know that it's a solution to the particular problem you're trying to solve.