There's a reason for the saying "Don't judge a book by its cover, or from how others describe them". I like to keep an open mind when meeting new people. If a person I trust and rely on said to be careful about another, I will keep their advice in mind, but I will still give the other person a chance. There are a lot of times where people just don't jive. It's good that this relationship with your client worked out for you and your company.
I've always found that information should never be wasted...hearing what people think of clients gives me valuable information...and not always about the client, also the person doing the talking. the way people talk about others says a lot about their own character and that can be valuable information to have.