How to responsibly/ethically confirm someone is in a consenting open/poly relationship?

Hi. I am someone who’s been open to and potentially interested in poly for quite some time but haven’t actually actively practiced it yet. I’ve done a lot of reading but I’m not as well versed as I’d like to be on the ethics and etiquette surrounding it, especially with how vast different kinds of dynamics there are.

I have connected with someone on a kink site a while back who’s been interested in meeting and potentially developing a relationship/dynamic. He is married, he is open about this and says he told his now wife early on about his kinks and things, poly was suggested, she was not interested and stepped away from their relationship but they ended up back together and married and she is ok with him pursuing others to satisfy those kinks but she wishes to remain separate and uninvolved, at least this is what he has told me and has on his profile. From what I can see, he seems to be pretty known in our local kink community and has had others he’s had relationships with people. He’s been respectful and not given me bad vibes. However, I know this does not mean that he couldn’t be fabricating the truth or lying which is my concern.

I have had past experiences with people who were cheating on their partners, some under the guise that they were open or poly. I contacted the partners in the instances I was able to but I just don’t want to end up in this situation again. But I want to respect the wife’s boundaries if what he says is true and so I’m just not sure how to proceed. Is is reasonable to ask to verification from the wife? Is there another way to do this? I’m asking this both for this particular situation and also just in general. Like how can you confirm someone is actually poly and their partners are consenting and that they’re not just cheating and lying? Or is that just a risk you have to take?

Thanks in advance for any input or insight.