A certified letter is good because they sign for it, acknowledging receipt, any other forms of written communication you can get to document that they were notified of the hazard probably also helps. 

I would keep and organize all of your communication around this issue, including gathering pictures of the unit and the area in question that was repaired.

Who ever imagined robots that are advanced enough they can create their own language to communicate with each other?

Just make sure whomever you work with is halfway competent and communicates well, the latter is the most important.

Other people are moved emotionally by them.

It's something similar kind of thing like we buy with our emotions and justify it by reason .2.

Also, try your best not to buy based on emotions (lol).

This frees you to focus on higher-value tasks like growing your portfolio, owner communication, and big-picture strategy.2.Adopt a Portfolio Management Structure: Early on, I ran a departmental structure (separate teams for maintenance, leasing, collections, etc.), and it caused inefficiencies and communication breakdowns.

It's a lot easier  logistics wise and the realtor will also probably have better communication with them since it probably wouldn't be their first deal together

Yes it does play on the emotions and it worked.