I charge a “day rate” + travel expenses. When a client wants you on-site, they’re basically using up all your time for that day–time that you might be splitting between this client and another client. So having you “captured” has an opportunity cost that you need to account for. Travel time is part of that as that too takes you away from other paying clients.
Never apologize for charging your client fairly for the services you’re being hired to provide.
w