Late Payment Policy

[mimi]

IMO you can charge whatever you want for a late fee. It isn't a loan and you are an independent business. I do think your charge is high, but if he signed your contract and therefore he is bound by your policies.
As far as slipping on your floor, I firstly would not have the door unlocked for a client to come in early, but if you do, I would post a sign on your door stating the floor is wet and for them to be cautious.
Lastly, I don't like clients who give threats, no matter if presented in a joking or veiled manner. Watch this guy.