Hey Sam,
Thank you for reaching out to us!
Unfortunately we currently don’t have a feature to prevent the submission of duplicate venues and organizers via Community Events form, but it’s a great idea!
I would recommend proposing this feature in our User Voice page to let us know.
Other users can then up-vote it, giving us a great idea of how much demand there might be (or, if you can find a suitable existing request, you can in turn up-vote that).
What you can do right now is to limit your users to choose from existing venues and/or organizers. You can enable this option by accessing your Dashboard and heading over to Events > Settings > Community > General.
If you have any other questions at all please feel free to let me know and I’d be happy to help as best I can!
Cheers,
Patricia