Too late to back out and go with other applicant?

[Jack B.]

So I had an application from guy A first and application from guy B second. 

Guy A has a much longer rental history and has a spotless record and would likely be a long term tenant as he has lived in the same place for 6 years. He is more easy going.

Guy B is putting deposit down tonight after his references came back good, BG check came back good though one arrest no conviction for a minor crime (DUI). He is a bit more aggressive. 

Both credit scores are equal.

I'd really rather have guy A, but guy B is on his way over because I fat fingered guy A's background check email and it got declined by the wrong person, so I assumed he was out. Turns out he never got the email and that's when I saw that I got his email wrong (which happens to him a lot apparently). But by that time guy B was told to come on by for a holding deposit.

Guy A would be a better tenant IMO but guy B is coming by tonight to put a hold on it. Too late to back out? I could just say I had a previous application and the results just came back in full, and technically to avoid discrimination I should take guy A's application, which is actually true, he applied a day before guy B...