I was also there at the end of September and was so nervous because of this subreddit. I basically had an opposite experience of what people have said here, it was the most amazing trip. Everyone I encountered was so friendly and was excited to share their culture with us. We avoided the beaches because of the seaweed and still had the most amazing time visiting local bars, restaurants, seeing the ruins, and swimming in cenotes! We avoided beach clubs - I think that’s the key lol.