In the case of the PM, social media and reputation damage can levy pressure on them, as well as use the BBB. 

My bank has waived monthly maintenance fees and unauthorised overdraft fees that our agreement entitles them to levy.

@Levi PainterThere are no absolutes, but generally the nicer a property is, the better your tenants will be.

I don't believe you would, but if you meet face-to-face the charge can be levied against you and you must disprove it...Decide by phone call first, then application, then personal meeting.

The judgment company will determine if your tenant is judgment proof or not and if odds are good to collect they might offer you 50/50 split and pay court costs to wage garnish or levy bank accounts etc.

Here a late fee can be no more than an NSF / dishonoured payment fee levied by the landlord's financial institution ... which is ~$50.00 across the major banks.As Marcia and others have said, a flat fee is much easier to communicate to the tenants and simpler to administer.

And if their creditors got judgments, that money is not safe in the bank, because it can be levied.  

For instance, if they've ever written you a check, then you know where they bank and can levy their bank account. 

Nobody likes working for a cheapskate and whether you actually are or not the people you hire will act on their perceptions.What would be interesting for a landlord like me would be if the PM wanted to levy a late fee  as it would be contrary to my policy of having them in the contract but not levying them.

I bought my condo. 6 months into living in it, a "Special Assessment" was levied to replace the boiler.