I've been doing taxes for ever, and thought that if you paid off your rental mortgage your taxes would be increased due to all of the rental income being profit (except for the operating expenses). 

The key factors here are experience (and how well that experience transfers to the property / business structure in question) and relationships.Using myself as an example, I currently own and operate 6 SFR townhomes.

There's many more factors to consider than simply purchase price and rents.

The novelty factor could be a plus in an Airbnb situation though.

The quality of the neighborhood and what's on the market will be the largest driving factors when the appraiser analyzes your home.

They do that to factor in maintenance and repairs.

They will also stay forever, and fight tooth and nail if you try to evict because they know they wont be able to find another Sec 8 unit available.Example, I just looked at 2 fourplexes in south troy last week, they havent had a vacanacy in years, the units are rented for 700/mo, yet the owners can't get 100k for either after a year on the market, and theyre decent buildings.

I defiantly will do it . all the factors that you mentioned are important and can really be a deal breaker for many .

I would say that 90% of the deals that look good on paper really aren't when you consider factors like rental comps, rehab costs, taxes, etc.

I have asked before, when I have submitted my documents, if we can order the appraisal right away because it does seem to be the biggest factor in delaying the timeline.