The small building next door produces 1k a month.

My partner does not think so because it is in an undesirable area, and, although property values are on the rise, this neighborhood will be the first to take the hit and go back downward when/if the market tanks again. 

How do I protect myself from developers from back-dooring me on this?

How small multi family  (# of doors) in Jax and what is your price point? 

When rents in your C or B class multi stop rising .Its a signal not noise. 

Currently I'm at $1600/door.

If your area is sketchy, maybe think of adding a home depot decorative metal security door to both front & back for single moms.

just keep knocking on doors and making phone calls, I finally got a good deal to sink my hooks in to and have your same issue, in the middle of a refi-cash out to buy this other property and the bank is throwing a wrench on the deal by asking me to pay off a car note to make the 51%DTI ratio. this bums me out but will keep pushing on until I get financing secured to nab this other property, maybe hard money to buy/fix and rent ( I am trying to avoid doing this), or maybe 203K loan, there are too many options, you need to exhaust all possibilities until you get one that fits. good luck brother.

I guess they'll not likely sell it for significantly less than they've listed it for, but if I plan on getting 1600/month/side, I feel like I could cash flow $100/door at a PP of around $305kAny thoughts around this would be hugely helpful!

I have set a goal to reach 100 doors in less than five years.