A duplicate sometimes happens when the connection drops right as you confirm: the app thinks the upload failed and republishes.
- Open your profile to see your listings.
- Delete the extra copy by selecting it and choosing Delete.
- Keep the better one if one has more photos or a stronger description.
To avoid duplicates, tap Publish only once and wait for the confirmation, especially on an unstable connection.
If you see several conversations with the same person in Messages, that's another known case we're fixing: simply reply in the most recent conversation.