Leaving negative reviews immediately after claiming products through the Vine program

I enrolled in the Vine program hoping to receive some reviews. However, unexpectedly, one of the customers who claimed my product through Vine gave a negative review on the same day, even though the item was not shipped until several days later. Furthermore, this Vine reviewer has mostly left negative reviews. I reported this to Amazon customer service, and their response was that it is not considered malicious feedback. Can you suggest any good course of action?