I have recently got a shady client, the order is about $300. So I have a question, the order is complete and the funds will be available for withdrawal soon, so suppose the clients disputes PayPal, and I have already withdrawal funds, can Fiverr dispute my PayPal to get the funds back ? Or can they only close my account?
No they can’t charge your Paypal. They will give you a minus balance if it happens, which it might not. It will look like this: -$300, or whatever the amount you earned is.
In addition to what @misscrystal said, they will not close your account. Your Fiverr balance will be negative, and your future earnings will have to cover that balance before you can withdraw a new amount.