Denial of Potential Tenant Application

[Justin Johnson]

I have just had two applicants that one does not meet my criteria, and the second does but the situation sounds very fishy and suspicious.  They have both used my Apartments.com listing to submit an application for the house, the first I declined due to my not pet policy.  The second, how do I decline with out potential legal issues?  They have zero credit, and a few statements they made during the showing raised some red flags to me.  Can I deny just solely on that even though apartments.com uses TransUnion for background/credit/etc. checks?  Do I need to send a letter to both applicants explaining why I denied their applications?

Thank you!