There are usually many signs to be picked but the often self imposed pressure makes many miss them; thinking “nobody’s perfect”, “I’ll manage” or “He’ll change”.
But from what is now a common trend, the change never comes.
There are so many things you’d be blessed to identify if you allow yourself to he open minded.
Many will pretend and lie about their capacity so in truth, you can either believe at a risk or verify that which you can. If he has a regular job role, his finance is easier to independently verify, more difficult if he’s self employed but regardless, you need to know what marriage means to you and let this be clearly known upfront.
Have your own financial plan, just in case. Yes, there are exceptions but I’m sure you know it’s no longer new to hear of men who married others with monies nonexistent or even belonging to another wife.
Beyond finance, you need to find out what sort of husband he currently is. This will be clearly shown in how he handles the Polygamy he’s proposing to you. Is he bullying his way with it, is he hiding it?
A man that hides you or bullies as an approach is already showing you all the red flags you need. This is how he knows to handle issues. This should also tell you you are more likely to meet a hostile situation on ground.
If his approach is to badmouth his wife or spend all the time with you, this already shows you one who is not trying to apply the concept of equity.
Polygamy is permissible for the Muslim man, however, the way and manner he does it will show you his reasoning, maturity and capacity as a man, husband and potentially husband to more than one. If you are having to sneak in, it says something about him, you, what you are creating and what to expect.
His faith is key but things like emotional intelligence, ability to communicate effectively, patience are key.
Run health checks and observations verifiable. Physical health, sexual health, mental health. Observe him under pressure and look at how he handles things.
Get premarital counseling whether single and previously unmarried, divorced or widowed because you are about to step into a compound system.