I am just a recent victim of this. I am a level 2 seller with over 300+ reviews.
I worked 4 hours on an artwork and the buyerr immediately asked for a cancellation 2 mins after recieving the artwork.
When i asked, they said they just want to cancel and they didnt even give me a chance to make any changes for them even though i had offered unlimited revisions. The buyer was being totally unreasonable. I declined the cancellation but the fiverr CS went with buyer and cancelled the order and it hurt my completion rate as well.
So, yes fiverr always goes with the buyer and does not care about the seller at all