Visuals usually sell better than reams of paper they have to read. If you can find a good healthy 4-6" sod plug, something 6-8" deep that has a good, rich, black soil look to it, and compare it to a core probed from their yard, you might be on to something. Explain the benefits of the richer soil (it looks darker and "better" because it has more SOM) compared to a light brown, sandy or clay soil. Now, if the yard in question looks nearly perfect, I would worry somewhat about pulling a core from the yard. You might find a soil profile that has flourished and will not be a good comparison for this purpose. A 1" soil probe that you can get a core sample from up to 12" deep is a great tool.