There are plenty of things Fiverr could do to reduce fraud, but Fiverr is a business so some features or actions that would be beneficial for sellers won’t be beneficial for Fiverr. Since there are plenty of topics on this I won’t go into detail
However, I believe that in most cases things go wrong because sellers haven’t taken the necessary steps to protect themselves (poorly explained service, miscommunication during delivery, unclear revision process etc).
Surely there are scammers out there who will try to get free work, but I think most buyers are honest and not every buyer who asks for a cancellation had that intention at the beginning. When things go wrong then buyers will try to protect themselves and a cancellation feels like the right solution to them when a seller is not able to de-escalate the situation.
I won’t write the long list of things you can do to protect yourself here because it would be just duplicate content to the hundreds of posts on this forum.
If you’re referring to the case you had a few days ago then that was most likely due to your revision process and poor vetting process. That has been answered and once you rethink how you manage your projects you’ll have fewer cases like that.
We all get scammers at times, but when this happens we come here, we rant, we improve the way we handle projects and we move on. Some might even send a complaint to Fiverr, but the key here is to look at the way you handle your business. That’s the most effective way to protect yourself.