True. I was focusing more on friends. In terms of shadchanim, it sounds like a big sheilah. On the one hand, as you say, who are they to determine that the person CAN’T get married. But on the other hand, wouldn’t the above halachos apply to them as well?
I suppose it would depend on the nature of the problem. For example, if she knows that the guy is physically abusive, then she probably is not allowed to set him up. A know a girl who went out with someone and then found out that he was being tried for the murder of his first wife. If the shadchan had known about it (and knew there was a good reason for the accusation), she probably would not be allowed to set him up.