One of the main red flags me and the leasing team look for is this type of behavior (picky or litigious).

It helps to have a conversation with a lender in advance (if you are serious...don't waste anyones time) to explain your situation and see if there are any red flags.For single family or 4 units and under a pre approval is also not needed but does go along way. 

If I went to a GC and said "Hey, take a look at this job and I will pay you" and they took the money, that is the red flag.

CA has the most red tape along with some parts of the PNW, NE US and a few other areas in the country.

if it was mine here is what I would do.1. walk in to planning department in the county and check zoning and any red flags they may have.2. should be simple enough to see if it has public water and sewer then call those agencies to make sure there are no moratoriums. 

In some states (usually red states), the laws are favorable for landlords. 

This is a big red flag for me, I’ve asked multiple times and haven’t gotten anything back.

When a applicant has a service dog or ESA-certified animal, is this considered a red flag? 

I still strongly suggest the GC--I don't know anything about Philly building codes but when I here big city, it think big red tape and your GC is going to be huge walking through the permit process. 

I'm rooting for you!