If you came here you'd be staying in a motel along with all the other undesirable people. 

College areas tend to have a steep gradiant between prime locations and undesirable ones.

Furthermore, HELOC loans' popularity may also stem from their having a better image than a "second mortgage," a term which can more directly imply an undesirable level of debt.[5] However, within the lending industry itself, a HELOC is categorized as a second mortgage.Because the underlying collateral of a home equity line of credit is the home, failure to repay the loan or meet loan requirements may result in foreclosure.

By that I mean a tenant who moves other people in, disturbs the neighbors or the city, has unauthorized pets or otherwise behaves in an undesirable but difficult to prove way.  

Recently  I have had two undesirable prospective tenant applicants flash cash before my eyes in an effort to get me to take them as tenants.

These checks are to protect you from undesirables - undesireables can be in the form of students too.

It sounds like your ad didn't set expectations (no evictions, no criminal history, etc.) of the tenant, so lots of undesirable candidates may be responding.

I don't think even the undesireable area of Decatur will get you there.

It really does not matter much with only a few rentals but as you grow in numbers and you have a higher number of undesirable tenant relationships or inherited tenants the advantages of M2M become very obvious.You are correct I do not invest in SFHs.

Usually when a place first shows up in MLS I will immediately get calls from the agents who have clients they can't place anywhere because they have issues that make them undesirable to landlords and ask if I can make exceptions, and they try to tell me how nice their clients are etc., to which I tell them if they meet the criteria attached to the listing in MLS there should be no issues and with Fair Housing Laws being what they are we can't make exceptions.