If there's obvious mold, then that should lead to investigation because there's likely a leak (or no air circulation).

Because they are so light and because of their shape they can float in the air for long periods of time.

Or worse...they aren't an investor at all...so they just pull numbers out of thin air!

The amount of air fare , hotel , rental car, was all a tax write off and well worth it. 

By the time I got to the house to observe the issue she had it all cleaned up but the funk was still in the air.

What types of routine or emergency maintenance will it need (water leaks / exterminator / smoke & CO2 detector maintenance / air filters / gutters / outside maintenance / paint / flooring / refresh between tenants, etc.).

This is a great little area ,it’s got a lot going for it as mentioned above plus they have started work on the $500 million judicial Centre ,a little east of here towards twin aire and if you’re feeling brave and have good risk tolerance and cash you could look at streets north and south of English near Twin Aire .Good potential there ,it will take time though 

Have you made any major improvements to the home like roof, replaced furnace, air conditioner, etc? 

Might just need a little work on the outside and there is potential for adding central air as it is currently set up with window units (very common in the midwest area I am currently looking). 

Other than it being smaller, painting a house between tenants is going to cost the same, a new roof will cost the same, a new air conditioner, hot water heater, furnace will be the same cost etc.For instance, it costs us about $1,000-$1,500 plus a months rent as a leasing fee. each time we change tenants, by the time we paint, do landscaping, repair damage, change locks, patch holes, paint walls that need to be painted get a make ready clean.