Don't you think the feedback system of ebay is flawed?

Of course, it is nice that buyers and sellers can leave feedbacks for each transaction, but how often are negative feedbacks are left indeed? For instance, I just sold an item on ebay; the buyer did not pay even after a month of communications. I am very hesistant to leave a negative feedback though, since that person may retaliate, do the same for me and ruin my ratings. Don't you think they should do smth so only the party at fault gets a negative rating?