Hello.
I think you should consider this perspective, as we are talking about services, mostly connected to arts.
Imagine you buy the ticket for a show in a theatre. You are excited because you think this will be a great show. But, after you see it, you find that show terrible. It's your opinion, maybe others liked it, but you are upset because you spent money for something you didn't like. Of course you can write a bad review (explaining what was wrong in your opinion) on the net, but could you get the money back form the theatre?
The point is also that not only we have some buyers (fortunately few) who try to trick the system, but in this way someone could have works for free. How can we control if they actually don't use the delivery that they didn't like?
It would be useful, in order to keep fiverr a community of fairy people, that seller can report buyers that probably are trying to trick the system.