Question for startup businesses and business coaches: How valuable would a business viability report be?

Hi Savvy SME's! I run a sales training and coaching business, and am thinking of launching a new product that I call a "Business Viability Report."

Here's the context: I'm talking to a person considering starting a service based business. They are interested in sales coaching, but part of my due diligence is to ensure they can make an ROI from my service.

Because of their revenue model, we determine that the business isn't worthwhile pursuing (and therefore neither is my sales coaching).

I spent an hour providing my experience and knowledge, and didn't charge for my advice. On the flipside, I have prevented them from making a costly mistake. I have also provided them direction for how they could change the model to make the business viable.

So here's what I'm wondering: How valuable is this type of advice to startups? Would $500 for a "Business Viability Report" be reasonable?