Skiptrace then hire a private investigator.

Should your tenants or their investigators ever come across this webpage (which I'm sure won't be difficult since your name is on it) they can use this against you in court should they choose to challenge your decision.

@Aaron LindenI am all for DIY, innovation and being economical because this seems to be a prior homeowner that did this or had it done by someone who obviously did not pull a permit since there is no way an electrical building inspector would have let that go.However when doing electrical work during rehab, whether for a flip or a rental, especially things that will be hidden behind a wall or ceiling that is not the time to cut corners - everything should be at the very minimum up to code both for safety and liability.Can you imagine if that Non UL Listed coffee can caused a fire and the insurance fire investigator traced it down as the cause?

I did a thorough investigation on costs and efficiency.  

Personally I do not know how to precisely calculate this but it would definitely be worth some investigation.

You can look up anyone here:https://www.myfloridalicense.com/sto/unlicensedact...Here is one guy that has already had issues and now under investigation for the second time.

The complaints will get faster investigation if the complainant(s) contact their state reps directly.

However, if you typically give a year lease, I would investigate further why this person wants to pay a year upfront.  

When the smaller apartment becomes vacant next I am considering getting quotes/investigating the cost of bringing it up to code.

And the assumption is that the further you move along investigating a property the more real numbers you will identify.