So your experience with a buyer is less than ideal. Maybe they were rude, or they nickle-and-dimed you, or they demanded extra work for free. Well, you might not get your time back, but at least you can leave a review on their profile so other sellers know to be careful, right? But do you really dare rate them less than 5 stars?
Providing anything less than a perfect rating would most likely ruin any chance of working with the buyer again, or at the very least it would sour the relationship. If the experience was so bad that you never want to work with them again, what might that person do in retaliation for a bad review? No one likes to be criticized, and sellers are not immune to sabotage.
It’s not necessarily something to stay up at night worrying about, and I don’t know how the buyer review system could be improved. But I do wonder how accurate it really is.