Seems like a gamble. Yahoo may terminate your account and refuse payment if they catch you doing that. But im not sure though. If it worked I would probably buy one.
Lots of invites have been sold. While it isn't illegal, it is against Yahoo's TOS. I started the new thread because I don't want people thinking I'm selling a Yahoo account (I.E. one that I have earned money in). It is the invite I am selling.