I acquired a property in Illinois that had higher levels of radon and it was as simple as putting down sensors to monitor. 

I am going to continue to monitor it as I think it will make a great case study of how greedy people were getting

I don't want to rely on guests to monitor the levels.

Let's get to it...I check my credit often since I have credit monitoring, and my current loan does not appear on my report.

(We also have a minimum profit # dependent on the ARV)I say currently using 30% because we'll periodically adjust the % based on other economic metrics we monitor.

I think that is always recommended and it is something I do.My inspector has uncovered things they werent aware of and has also alerted me to issues to monitor to make sure they are rehabbed properly (for instance ensuring that the electrical scope included adding additional circuits because the current number was deficient).

Snow removal and de icing, require or offer tenant insurance, document applicant refusals or evictions and reasons, require and monitor fire and carbon monoxide alarms, no trespassing signs, tenants only, no subletting, etc etc.  

I would step back, tenant is paying, look at how the place is kept, adjust rent and monitor performance under month to month. 

I may even consider a credit monitoring and or repair service to really get that in a strong position.

You do the best job you can to screen and place, you monitor, inspect and hold tenants accountable but at the end of the day you have zero control over the outcome.