I ask prospective employees if they are bondable. Their answer to that question will let me to know if they have a criminal record or not.
I guess the best way is put yourself in the customer's shoes. Would the customer be comfortable with a convicted felon working in their home or business? I would say that people would have a problem with someone convicted of murder, robbery or sexual assult.
The nature of the crime would be the deciding factor on hiring. Is their past going to hinder the business?