This is probably quite harsh for most people, but if I get a less than 5 rating I block the user after a little while. If they were in someway unhappy with the service provided and didn’t communicate anything to me at the time, I’d prefer they didn’t come back. Even if they did communicate, I still might block.
I undertake fiverr work for the fun of it in my spare time and like the fact that I don’t have to strike up a long term relationship with a buyer if I don’t want to - even if missing out on repeat work. If there’s the slightest hint of hassle with a buyer, I’ll block them to avoid a repeat.
I hear so often that fiverr favors the buyers and sellers should accept how things are or move on. Yes, maybe. This is how I keep it interesting for me.