I like the idea of asking questions to the group to help them identify potential challenges that are both relevant to the issue area of the group and could be addressed by your seminars. From there you may be able to facilitate a consensus building approach within the group towards effective problem solving addressed by your seminar. Perhaps making the problem solving being about getting everyone together in one room to address the shared challenge rather than it be a 'salesy' seminar pitch is best. That way there's ownership among the group to help develop specifics of the seminar content and you are positioned to be the convener. Happy to discuss further if interested.