You're selling to someone in your state where it's legal. You don't know these people so no matter where they tell you they're from, you have no way of knowing if they're telling the truth.
The ban is by species so the half dwarf is covered.
For all you know, it may be a set up, so just let them do what they want with it after the sale, don't ask where they live or where it's going to be kept (if you do ask then you're complicit) do everything nice and legal, no shipping, no crossing state lines. In this instance you are not your brothers keeper.