You won’t get it from the existing tenant as they magically will not be able to afford an extra $100 a month - so if you raise it you will have no occupancy which at end of day neutralizes rent increase3.

On the first contact, I make make it simple and neutral.  

For the floor, you need to neutralize the whole thing.

Additionally, I've seen the banks start to do some minor rehab\freshening up of this type of home, exactly what appears to have been done here - new stove\microwave, carpets cleaned or replaced with builder grade, some fresh neutral paint etc, in hopes making them more appealing and moving them faster.Also, the lot seems tiny, less than 1/10 of an acre, and there do seem to be A LOT of recent foreclosures in the immediate area, which may scare off some buyers.

You can you passive losses to neutralize/eliminate passive income.

Lessons learned: At today's interest rates, this exact same house would be around cashflow neutral.

It’s pretty neutral, which makes it a safe bet.

It seems to me as you add properties that are cash flow neutral, your Debt / Income ratio will continue to go up and up, even though your ability to pay will not decrease. 

As of now, it looks like I'd be anywhere from negative $500 per month to cash-flow neutral.

Like @Nathan Gesner said run an ozone machine, and you can purchase specific odor neutralizer sprays like car companies use.