I  personally wont work with a non licensed person simply because its infected with to many beginners who don't really know the industry have no clue and are huge time sucks.. so you have that barrier .. or the wholesalers that are proficient but they sell to beginner investors who are chomping at the bit and will over pay ..

If they go crazy on it (maybe because more of the tree is over their property) and they cut it too much the tree can die (heck, if you are not careful in the trimming process and seal the cuts, it can also get infected/infested, end result same, dead tree later) or worse, become unbalanced and prone to crashing on your property or his - so make them aware of that.

Then a small dried out spot on my foot turned to full blown infection that cost me my right leg below my knee.

Took one day for him to end up in the Emergency Room at Tampa General with a huge, infected, boil from the Brown Recluse Spider that bit him.

You can get a mold treatment chemical or mix bleach and water and spray it onto the infected area.

I actually just ran into a HUGE issue with a private blog I manage (not a Carrot website) where it was infected with Malware and my hosting provider gave me 3 warnings and shut down my account.

HPS is a rare (only 20-50 cases per year in the United states) but deadly (40% mortality rate) disease transmitted by infected rodents through urine, droppings, or saliva. 

Also, laundry detergent should be used, "Low Suds"...this has to do with NOT upsetting the GOOD Bacterial process that should be taking place in the system.

The poor baby probably has some medical problem i.e. infected and plugged ears.

These have a finite shelf life and tend to degrade form the inside, so you know you have a problem when you see water, a high bill, or bacterial growth.There's not really a one-size-fits-all answer here, but rather you can learn through the process of doing and figure out which ages of homes you are most comfortable with OR you can invest in new construction and newer homes.