Not all of them. I have never asked for a review or even mentioned a review in my time on Fiverr. Yet, without guiding my buyers, I have only received a single 4.7-star review in the last two years.
I think it comes down to being able to spot red flags in buyers. We're competitors, OP, and I can see that one of your recent 4.3-star reviews came from a buyer that I turned down because he seemed like he would be too demanding. It's about learning what signs to look for.