Sigh.. who wouldn't get annoyed by someone spamming a chat making it impossible to read what others are actually saying? I'm trying to sell something and someone is spamming it away so that no one can see it, but if I get annoyed by that I'm not mature? What if I saw a Pokemon go up for sale and I didn't catch the guys name before it got spammed away, I guess I must not be mature if that annoyed me too? I don't know when maturity levels started getting gauged by what annoys you, but I think it's quite silly.
Anyway, it does seem difficult to prevent abusing your suggestion unless there was some kind of system put in place alongside it. For instance, something that only toggles the voting for people active in the community? I have no idea lol