In short, my lawyer also would like me to use a 25 page contract with hundreds of disclaimers, but we both realize the practical limitations of such, and have agreed to keep it to one page.
Providing the additional service does not add any time, as I would have spent that time on-site answering the same questions (as you indicate). By doing so, I engender the same level of trust, and clients do get to know me, just as if they were at an inspection. No increased time, no increased liability for those reasons - no need for a surcharge.
If I have not had a chance to evaluate an item yet, I say so when asked. If I have, I don’t mind taking a minute to back over and answer what was asked.
I always ask after completing each floor if there are any questions about whatever was on that floor that we covered. But generally they have asked them as they occur, so there are few questions at that time. However, occasionally, someone will think of something out of the blue, and it really takes very little time to go back and answer the question, then continue on.
For the extra 15-20 minutes this can possibly take (almost never takes this much time), I have created an atmosphere where clients know I care about them, want to answer their questions, and they feel encouraged to be active participants.
In the end, it is my goal to make clients feel comfortable using me as a resource - not creating some professional distance so that they feel like they have to raise their hand to ask a question, or wait until I say so.
Everyone handles it differently, of course. Personally, I am pretty relaxed and informal. As an inspector, I am not very rigid, I make the client comfortable and encourage their questions, and I market to this point.
Incidentally, it also tends to takes the “scare factor” out of the inspection process and humanize it, which impresses Realtors, and relaxes clients somewhat so that they listen and understand the information.