- How do you argue? Is your partner denigrating? That’s a personality trait and an immediate no.
- Do they have an addiction? If you are married, you can try to work through it if they want to get better, but statistically it’s a long shot. But if you are just dating, why bother?
- Are they materialistic? Are they just in the relationship for what you can do for them?
- Are they honest?
Etc.
Granted, even this information gets tainted: narcissist parents, for example, might come across as their parents being nice, but them not being nice to their parents.
You can tell a lot about someone by how they treat someone they don't like. Some people get downright cruel with people they don't like, and it's a huge red flag because some day they may find reason to not like you. You're just setting yourself up to become a target once you find yourself on their bad side.
You sometimes see this when someone's hating on a public figure. They insult the person's weight, appearance, and speculate about their sexuality. I am never surprised when these people turn out to be abusers and harassers.
Trust me, if you stay married long enough, there are going to be times that you don’t like yout spouse and vice versa. That’s when you really see what you are both made of. Over time the rebound either gets faster as you learn how to disagree civilly - or worse.
I think this is also why words of affirmation and acknowledgement are so important, like taking the five seconds it takes to say you appreciate your partner, and thank you for clearing the table after dinner yesterday.