How do i charge so that i know this buyer is as serious as i am?

[Ryanna Masiva]

my potential buyer wants land. I found some options. Now they want to visit the land. How much do i charge for my time if they now want to go see it and trusting me to go with them? I guess i need to make sure their serious and im not putting out all my effort to help them. By the way their willing to pay Millions on this land in Maui. Please help if you can. Is there a fee before closing and all that? Whats standard?