If they were selling for less, then you have more downside risk.Now, I have no real evidence this is an accurate way to look at this problem.

If you gave him the previous appraisal at 548k and he came in at 450k he did it because he felt he had good evidence.

If there are stains and smells save the carpet and take it court as evidence if need be.

I hand delivered evidence of transfer, new servicing information, RESPA, FCRA, FDCPA, UDAAPs notices upon my visit.

In Oakland, California, if a resident indicate a disability check is delayed, we must accommodate that resident if we receive notification of evidence.

Send a letter to him explaining there is no evidence of mold or current leaking and therefore you are not replacing any wood and he needs to pay up by XX date or you will start the eviction process.

I've not seen anything to support either side of the coin, i.e. no evidence that an attorney would or would not be able to "pierce the veil".  

Some of those items might be major and require re-negotiation (which you now how evidence to support).

I'm not sure the handyman's anecdotal evidence is sufficient to make an $800 investment.

You will ultimately regret having this tenant based on their present behaviour.The upside for you is since they do not have a lease signed by you they have no evidence to argue otherwise.