And it should have a section devoted entirely to some sort of Success Probability Rating, or a similar equation that says if this happens, then that should be the expected result. As a prospective buyer, you might wish to do the same to make sure the price quoted was indeed fair-market value. This experience almost echoes that of thousands of inventors every year. A professional appraiser will either save you money or make you money, based upon the recommendation he makes that you follow. If your property investment, whether real property, intellectual property, or otherwise, is not worth the cost of an appraisal, or putting a little money into, then you really should have no business being involved.
Free rides are great, they generally generate a good memory, but nothing of long-standing value.
Prices for evaluating inventions will vary, much as the technology involved varies. Solve as many of the market variables as you can before you submit the idea for evaluation. This will save the evaluator time, and that will end up saving you money. I have offered free evaluations in the past to all independent inventors that wished me to review their ideas. I am pleased to have formed a friendship with this group, it shall bode well for my inventor friends in times to come.