@Colby Mulry
I checked online and discovered there is no limit to late fee in Rhode Island. Check your lease to make sure there is not a maximum late fee. Start charging 8% or 10% immediately for every late fee. In Minnesota, I charge 8% after midnight the first, no exceptions, no matter how much I like the tenant.
Also, don't do written checks, if at all possible. Two of my tenants don't even have checking accounts, yet they pay every month at Cozy. Hearing their excuse is a waste of your mental faculties. Just follow procedure. Hit them with the late fee, and make it sting. Send the late notice letter the day after it is late. Call around to find out eviction costs, and communicate the costs to him/her for the eviction if it comes to that.
On the bright side, you have a paying tenant who at least pays every month, and if they don't mind paying an extra 10%, and they take care of your place, maybe you just decide what your tolerance is, and go with what you think is best.
Lastly, if it ever comes to eviction, it is not as bad as people make it sound. Find a company to do it...ask property management companies who they use, or other investors. Very likely, someone has a contact where the lawyer or company does all the hard stuff of the eviction. If they do damage, it's part of the dance.
Also, consider cash for keys, if you want them out. First offer I give is I will refund their damage deposit the day of the walk thru, minus any costs I estimate on my final walk through. They get a check, you get the keys.