I remember once reading that the most beneficial service to a tree would simply be adding woodchips around the base.
I was thinking of buying a penetrometer and being able to put a number and visual for clients.
I was also thinking about not giving free estimates anymore for anything other than removals. Instead, I would offer a basic consultation, with a pre-determined list of ''test'' that would be done: 360 visual assessment, basic measurement, sounding with a mallet, penetrometer, soil and tissue sampling for test, if need be, all put down on a simple checklist kind of report. This probably could be done for a fixed price in most cases, let's say 100$ for the first tree and 60$ for any other tree after. Just rummaging here....