If I get an order for one of my very local areas and it is a no find and they cancel it, i am ok with that at no fee. BUT if it is a no find for an outer county or a not so local area I charge a $20-25 trip fee.  And if I finish a search before the due date and it gets cancelled I send it in with an invoice for half the fee as a completed order cancelation fee. Also, when I do that, I mark accross the entire search the words order cancelled, may be incomplete, so that they can not use my product for a closing.
I have never had a problem collecting those.
I have never added late fees either.  The treat of filing suit for the amount owed ususally works for me.