(Many people do this.) 6 months later my roof leaks again and I put another claim in to my insurance carrier.

Don't tell them you want new carpet, but things that impede your ability to feel safe and comfortable- bugs, leaks, mold etc.

Usually If the roof is leaking they'll just tarp it to protect it, and most won't even do that without constant pressure from the listing agent.

This means a roof that does not leak, hot water available, heat and air conditioning, and good plumbing / electric.  

I changed a water heater, huge leak in one of the units, electrical issues, and I even had to dig a 3 foot hole under the house and personally fix a pipe.

So he told me what to offer and it was accepted.That said, the home had a lot of hidden costs because it was vacant and everything was shut off, that it was hard to detect up front.  

Mold is caused by water.. you have to stop the cause of the water which is usually pretty easy to do if it's a leaking pipe or a busted roof.

Especially the days when you discover that big capex like a roof being blow off (happened 2 years ago), some tweakers climbed up on the roof and gutted the A/C (did two of those in the last 12 months), an evap cooler leaked for so long that the drywall on the ceiling of the kids bedroom caved in (last year), the hot water heater blew a hose and a major leak went unnoticed for 10 hours flooding the hall, kitchen and living room (dealing with that now), the tenant smelled gas outside, the gas company came and shut off the gas because the underground pipe is corroded AND also discovered that the water heater is not venting properly so it got red tagged (just dealt with that last month) or the time the tenant "invited" a homeless guy over, he moved in, then called his other homeless buddy up and he parked his crappy RV with his entire family living in it in the driveway.

I have a building right now that's leaking water into people's unit but the owners won't do anything about it because they don't want to spend the money.

There are many tests that need to be conducted to ensure the land is not contaminated (the tanks always leak).