It's not about 'fair\unfair' stuff - it's about understanding of how admins are running the place. If rules are unclear then it's also unclear for everyone else on how to follow the said rules. The lines like 'don't troll or ban' or 'we'll ban you if we feel like' just breaks the wish to invest any effort since you can't know for sure if it's allowed or not.
Rules must be simple and clear. Special cases are allowed anyway as you said - but RULES must be clear for those 99.9% who are not 'special case'.