Since part of your property is a rental, I believe a portion of your mortgage interest should be a tax deduction unlike your other debt.

Let's assume that the neighborhood is a C class and the median income of the city is greater than 3X of the market rent.Here are some of the considerations I've come up with so far:- Units are in need of renovation and capex is too high or not available- Unit quality is not the same as market - Seller is worried about losing tenants due to increase- Vacancy rates are high or filling units have been difficult- Rent increase would take multiple increases over multiple lease periods to get to market rate if seller is trying to retain the same tenant- Seller inherited property and just want to liquidate- Seller needs to liquidate quickly (financial burden, sickness, quick exit from land-lording)It seems like I might be missing a warning sign about a deal if they are selling with current rents that are under market; but again, this seems to be most of the properties I've underwritten.And in the same vein, what should I be worried about when purchasing a deal with under market rent with the intention of raising them after purchase. 

I recommend that you find a trusted or recommended Mortgage Loan Originator (MLO), who can give you options for property-based loans (mostly investment loans) and they don't use your taxes but the P&L of the property.

And this low demand could be a couple of factors, either a rural location with low population density or the area incomes are not high enough in order to prevent a rent burdened scenario. 

I usually run several CMAs, with different criterial, and of course compare tax appraisal value with a wholesale price, add 5% as a fee to a transaction, in some cases.

Most Florida markets will share some dynamics though like taxes and insurance. 

Out of my 32 properties, I’ve seen insurance rates drop by up to 40% on renewals, and property tax increases are finally slowing down compared to the crazy jumps we saw over the last five years.

He is busy working at the hospital and doesn't want to deal with tenants, toilets, taxes, trash, and all that haha

Bear in mind that the fiscal treatment of the two options in Mexico is different (withholding tax on the gross income with the fideicomiso vs cost deductions with the corporation).

Usually the numbers don't work to build in these neighborhoods, unless government tax credits, etc.Do you see the problem with your two statements:"The turnover costs could/will be high"and"How much more damage could they do?"