Engagement
Attendees can just simply log off and leave should they wish. They may not be as engaged with the event as much as if they were there staying at the event for the day, over night or for the weekend.
Atmosphere
It will be harder to create a 'buzz' as many human senses will be neglected.
Interaction
Interacting at a virtual event will be harder as it will have to be conducted purely through visual, audio or messaging which could cause misunderstandings and breakdowns in communication.
Internet Connection
Reliant on everybody having a reliable internet connection. Connection or technological issues could severely impair the experience.
Technological experience
This platform assumes everybody is computer literate and comfortable with attending an online event. There will be many demographics this will not appeal to and therefore could exclude potential buyers or sellers.