If rents dropped $50 a month because of an economic downturn, you would suddenly find yourself going negative on cash flow on this particular property.

The statistics on this cohort are misleading. 

@Meghan McCallum I doubt seriously that any such invention exists, as the statistics on stock picking versus indexes are abysmal.

To minimize the impact of that data-point, and thus minimize (or, ideally, negate) any appraisal shortfall, you will want your Realtor to host the appraisal, and you will want your Realtor to provide documentation (not words, docs) supporting your low low purchase price as having a really good reason. 

If interest rates and, hence, mortgage rates shoot up that will be a negative for housing prices.

The only negative I can say is that their materials were dated and had some typos in it. 

If that’s the case that will negatively affect my ARV, didn’t anticipate that..If I chose not to do anything, could I still sell it in a few years or I’ll run into a buyer that will want me to rectify this?

Since you brought up weight-loss products, what is the reputation of such products that do not work as advertised (which is probably 100% of them) - awful lot of complaints and negative reviews.

If we eliminated property taxes houses would appreciate (although the ancillary consequences of eliminating property taxes may have a greater negative impact on property values) because people could afford to pay more for the house. 

It is basically a natural plant growing, so don't think it would have any negative effect on the condition of a home.