My new responsibilities leave me little time to post, so I figured I'd dump a quick PS execution for admins quickly searching for a way to avoid double booking in their environment.
get-mailbox | where {$_.ResourceType -eq "Room" } | Set-MailboxCalendarSettings -
AutomateProcessing AutoAccept -AllBookInPolicy:$true -AllowConflicts:$false
ResourceType can be substituted for other types than Room as well.
