Fiverr is trying to improve the integrity of the review system. In the past, there were a number of ways to get around bad reviews: offer cancellations, harass buyers, offer freebies, etc.
Now, Fiverr doesn’t want anybody playing around with the system. Buyers and sellers both review a transaction once, then it’s done. If a seller tries to cancel an order to avoid a bad review, or asks a buyer to change their review, he or she will likely be slapped with an account warning. If a buyer asks to change their review, this request will usually be denied unless the review is abusive or was the result of a technical error.
Here’s a quote from the Help Center that explains Fiverr’s current philosophy when it comes to the exchanging of reviews:
To maintain the integrity and quality of our marketplace, we ask both sellers and buyers to provide their reviews after each order. It’s important that these reviews are honest and independent of any outsider pressures, giving both buyers and sellers a chance to learn from candid and thoughtful reviews.