Time IS Money
I charge by the sq ft and by what I'm inspecting. I use a "range" type of setup. $X.00 minimum, up to 2K or any condo (since there's no roof-crawl-exterior) add for 2001-3000,
add for 3001-4000 & premium for up to 6000. Over that is base + per sq ft.
Extra for pool, any guest with a bath, add for bath and kitchen, pool, add for pool + spa. No difference for slab vs crawl. Charge like all were crawl. Still have liability for slab just get a little "freeby" for me since no crawl.

If someone grossly misrepresents something I will add charge in the field or not inspect the extra. They usually go for the add-on. This usually happens when they don't call out for "guest" when it is obviously a discrete guest area with it's own facilities. I don't bust their b**** about it. Sometimes only "mention it" to the agent that called it in and do the little bit extra free "this time only" if it's not all that much extra. Seat of the pants call in the field. If I feel that they are trying to take advantage of me, I charge, usually more than called for just to "slap them upside the head"