You can visit modlog to check whether the post has been deleted by moderators or the poster.
If a post is deleted by moderators, it should be listed in modlog. Simply, Ctrl+F and search for ID of the poster.
According to following post made by Halab, if a report is handled and the post is deleted, all other reports for that post are also deleted and they all are marked as good.
If the solution is to move a topic, the mod must click 20 times on 'handled' after moving the topic.
If the 20 reports are considered bad, the mod must click on 'bad' 20 times.
According to what Halab said, only if the report is bad, moderators should click on "Bad" for all reports. So, when a report is good, all reports are marked as good automatically.