You know, I was thinking... something that would be good not only for the gilsellers issue, but overall socially would be that blacklisting would work account-wise, not character-wise.

Think about it. If there's a person I don't want to contact me they can always make a new character and contact me again, which would be unfortunate. I want to block a person, not a character. In the specific case of gilsellers this would mean that after I block them they won't send me a tell 10 minutes later from their new char, and that may reduce the frequency of spam. This and a right click -> blacklist/report feature would work very well I think.