Fiverr updates your rating regularly, so you bury bad reviews with good ones.
Also, if you think the review is very unfair, then put a polite reply explaining your side.
Honestly 100% good reviews can look a but shady.
Not everyone does; I don't, but because you advertise your rates rather than bid for jobs it can force prices down. Try offering multiple options and build a good overall price for a job. Like a burrito place that makes its money by charging extra for guac. Also be as unique as possible, give people a reason to pay you more.