Please refer here: How To Tell if your Name is Rare or Not + Name Market Tips/FAQ The 's' making it plural takes the value out of it.
What makes them the deciders of how rare or valuable a name is. Its all about a person's interests and desires in a username, if they want to pay 1b for one they can pay 1b even if to you it may not be worth that much but to them it is. Being plural should not make it worth nothing and Sythes mods seem to think they own the decision of making worthless rules for Runescape that effects someones selling point, don't interfere in someones sale. I could easily find a website to sell my name on it for what I wanted.