That still shouldn’t deter you from talking to them. If you tell them from the start that you already know something about the Church, and probably not be interested in joining, but would like to hear their message anyway, they would be glad to visit with you and share their message. They get so many rejections that they will be glad to have someone listen to them for a change!
I wouldn’t say so. Perhaps “how it goes” would be a combination of what personality type they are and how their message is received.
I joined the Church as an adult, and was beyond the age of missionary service; but there are plenty of returned missionaries around who can share their experienced with you.