Mean-spirited people don’t stop being so in a relationship and may attack your self-esteem by latching on to what they think are flaws in you. Now how much of a blow these red flags deal to your relationship is down to you.
The person needs to be acceptable to you as he or she is. If the person is in a lot of debt, or tries to "borrow" money from you, beware. It's not always easy to determine if someone is lying or withholding the truth. If you consistently feel that you are not being told the truth, and you have not been concerned about this in other relationships, then trust your feelings.
They will change if they want to, but you can't make them change. Many of my very kind clients, in trying to help their partner, have been used and burned by loaning money, or by allowing their partner, who is not earning money, to live with them. If you have a trust issue in general, then you might want to deal with your issue. The person has no close friends and is not close to family.
Often ‘red flags’ are a character trait, for example aggression, and at other times it’s a fundamental core difference in values, indicating something that’s extremely important to you that you really shouldn’t and cannot ignore.
Red flags can and often will deal a fatal blow to the relationship.
Unless this person has had a good amount of therapy and personal growth since the last relationship, a series of broken relationships or marriages may indicate that he or she doesn't know how to have a loving relationship. The person was abused as a child and has not had therapy or done sufficient inner healing work. Without an openness to learning about themselves and you when there is conflict, there is no way to resolve conflict. The person participates in addictions that are unacceptable to you -- smoking, drinking, drugs, addictive eating, gambling, TV and so on.