Parady falls under the fair use part of copyright and as such is a defense not an absolute.  For something to be considered parady it must make a statement; political, social, comedic or a little of all; it cannot be slanderous.  Vendors selling likenesses are not protected under the parady exception, neither are people that give them away.

Advertising is not a grey area.  Without the celebs concent it is not allowed to use their likeness or voice in an ad and may lead to a simple cease and desist order or a civil lawsuit.