How well qualified are they really? From what I understand, you may not deny based on the "service dog". The clowns I've gotten with a service dog wouldn't even allow a credit report. So there's a denial right there.
I know, I know. We live in Russia. Before you know it won't be politically correct to keep your rent money either. It'll all have to go to the government. Oh yeah, we already do that.
Stall until you find another legal reason to deny. Credit? Income?
I always use the reason that another more qualified applicant was accepted. If asked for a specific reason, I tell the truth: Income or credit.
LPA denial letter or if because of credit report adverse action letter.