I have also had tenants do work that they said was free at the time, only to come back later when moving out and try to charge me.

If you didn't over-pay for the house and he didn't charge you closing fees I'd just adhere to w.e he says....Your best bet is to post on Avvo and see what the lawyers say (its free).

What if the tenant comes to them with a valid explanation, such as an unexpected car repair, etc?

s) but if they direct deposit they can make a small deposit and it will be considered accepted and nullify your case.Also, make sure you are charging a late fee 5% in NC that seems to motivate people as well. 

They usually charge several $100.

Plus, I'm pretty sure they were charging me for inspections they didn't do.

I frequently see the 50% rule on expenses (sometimes 55% on BP) so this could set you up for some unexpected surprises in the future (specifically with CapEx).

Unexpected things always come up so the thinner the margins the less room investors have for speed bumps along the way. 

The Civil Rights Commission will assign an investigator to see if there is cause for a charge - they do not operate on a "guilty until proven innocent" basis.

@Franka HauckAndrew gave you some valuable tips.A couple things to keep in mind1) Charge market rent to your inlaws.