Are you a bot?

Recently we opened our community platform to everyone, and saw some really interesting new user behaviour. Some context: we are a community that listens to music together. People start their own sessions, and existing community members can hop in to listen along, and hangout. It's a great way to meet people. Interesting, a lot of new members felt that the existing community members were bots! Why? Because they were so nice, and we were genuinely stumped when we realise this. They thought real people can not be so nice from the offset. We never faced this trust issue when we were a closed community. Have you ever had a similar experience with your own community? How did/would you solve this?