Recently this happened to me. I sent an offer to one of my buyers. And he accepted it. And instead of 1, i got the same order 3 times with different order numbers. This is for the same single offer i sent.
And now the buyer asked for a refund for the 2 extra orders he made, guess what,
I got my order completion rate reduced instantly and my rating is affected.
I lost the chance to cancel an order that really should cancel later days because of this.
I have contacted customer support regarding this, I will update the case in here.
UPDATE : Fiverr support reversed the order completion rate!!