I have to agree with lvl 15 to be able to use shout and yell but then they will just be spamming in say instead :P
and that wont stop them from spamming you in tells also,

ive already blacklisted gil sellers sending me tells added them to blacklist and pretty much 2 minutes later spammed again with a different name,

these gil sellers areh acking peoples accounts stealing everything on it, then using there accounts as well as there own to use as bots to advertise there gil,i highly recommend everyone get a security key/token addedo n there account right away.