I am going to answer this question as a former sales person plus as someone who produces content and train sales on new messaging. Sales people will listen to you if (1) they feel that you can help them close deals (2) you understand their painpoints as a sales person. So two things that I have done, which makes my training effective. (1) I make it a point to join calls as a silent listener, and when I train a team on some new messaging, I would reference the call that i attended as an example on how / why new messaging might be more effective on said call. A complimentary approach to being on calls is to leverage and befriend a top sales person and work with them on the new messaging. Have this person to test new messaging and work with them till they are successful. Then leverage them in training because reps will follow the rep that closes the most deals.