Check the screenshot of the comment received from a customer. Also, this person haven’t purchased our item.
What are your thoughts, how to handle them?
you have already flaged the comments, good joob. 
if they again do this type of crazy comments you can report it to author support. I have checked their profile actually they don’t have any activity as an author or as a customer.
Still this customer keeps posting spam comments ocassionaly, if you have the rights then check all this previous comments.
report to Author Support. they will take care this.