Answer

I don’t blame them. I don’t believe a lot of the puffed-up projections of benefits that I have seen, either. The answer is very simple: Your client, not you, needs to estimate the value he or she expects from successful completion of the work. You must have a clear and candid discussion with your client about value, and you may need to push them a bit: "What do you think it’s worth to your organization if you solve this problem (or capture this opportunity)?"  "I understand it’s hard to estimate, but are we talking about $1 million or $10 million?" And so on. Your client must own the value estimate.