The unwillingness to provide the last three year tax returns and agree to a credit and criminal background check would be a great turn-off.
If I was looking (I hope I never am in that position), but if I was, this would be a baseline requirement of any long-term committment.
Watch enough of Snapped and shows like it and that will show the need for both of the above. I find that if you speak with people long enough, you can figure out red flags without the need for credit or background checks. People reveal a lot if you give them enough rope and time.