Must a landlord perform background/credit checks on prospective tenants?

Simple: it's much easier to work with experienced investors who already have lots of experience and capital.However, that should not deter you.

@Clinton Holmes Similar to @Deborah B. we set out with intent of serving specific demographics: in our case, students and young professionals.At the moment, our units are ~60% student, 35% young professionals and 5% young families.The most important thing you can do is screen your tenants:  We provide all prospective tenants with an application form which includes a guide explaining our application and tenant screening process and what information must be provided before an application is considered ready for processing.  

I have a short sale prospect that I am working on.

Totally uncalled for actions- flipping out and yelling at a prospective customer?

DU ( Desktop Underwritter ) and LP ( Loan Prospecter ) are still approving DTI's over 43%As long as banks are getting approvals and they have no overlays they will fund deals even if they're over the 43% range. 

From my prospective from a real estate agent that works for a national wholesaler, the non-refundable deposit serves many purposes.  

Keep in mind that, unlike real estate, a prospective buyer gets to see a lot of really personal information about our borrowers.

I currently have 3-4 prospective multi-family homes that I am looking at with great cash flow already in place, what should I do next?

I'm just getting started with my marketing campaign to look for prospects and my first check.