Reject their application on those grounds.

To my surprise, the contractor told me based on his experience, there's a slim to none chance of getting this installed, especially in Boston, because we would need written approval from the condo association and they would likely reject it partly due to work being needed in their unit as well to get this installed. 

This one would be very straight forward for me- a reject based on her income level and length of employment.  

Although some reasons may be in conflict with fair housing I don't really care when protection of my investment is concerned.I would guess that:1) they had low credit scores if any score.2) each alone does not have sufficient income to qualify for the rental by themselves.When screening young unmarried couples each must qualify fully on their own merit otherwise both are rejected.

Be careful if you reject an applicant based on personality because his old landlord didn't like him, you could risk running into discrimination claims - whether it was intentional or not, you would still be in trouble.Here is a link to an article about how to create legal and objective screening criteria, including using landlord references for verification. https://www.rentecdirect.com/blog/2015/10/how-to-c...

Unfortunately I was rejected. 

I plan on rejecting the applicant after they have already applied.

Keep in mind aside from non payment of rent the majority of board applications by landlords will be rejected.

We will have to see if Freddie rejects short sales minus any requested buyer verification.

A tenant with no landlord reference or with no credit would require first, last, and deposit.Tenants with no Landlord reference AND no credit are rejected.