More sanding means you get closer to the original wood color because stains only penetrate so far. 

Water based sealers are far inferior to oil based as far as lifespan and penetration.

Climate - Properties in areas with hard freezes and excessive moisture will tend to require more maintenance than in milder and dryer climates.Age of properties - The older the property, the more maintenance it will require, unless all the major systems and components have been updated recently.Property cost - There is a tendency for new investors to choose locations with very inexpensive properties.

Avila-I installed a light/fanswitch that has a moisture detector on it where the fan will turn on automatically when a certain humidity is reached and it automatically turns off later.

A partial list was , fireplace built wrong unsafe , no electrical disconnect on outside of house , no gfci breakers in bathroom , garage or outside outlets , moisture around foundation , basement steps not built to code , no escape window in basement .  

The contractor is assuming previous insect damage and rot from moisture.

I informed her at move-in that the floor was laminate and should not be wet mopped or exposed to prolonged moisture.

The swelling is from the moisture so probably no question the moisture got in there, but how much biological growth it grew is questionable.

Originally posted by @Meir Sasson:Thanks for the info.Gary , regarding the extension life of the roof without a gutter, the roofer is claiming that since the water don't move down in a clogged gutter it is ultimately damaging the roof, soffit and fascia.Meir Absolutely a problem up here...in fact we have to put roof deicing cables on many roofs to avoid ice dams pushing back moisture under the roofing tile then into the interior & also destroying the facia.  

Many plumbing issues can result from roots penetrating sewer lines which should never be the tenants responsibility 8.