Are you saying that you shared a Sim with this person that had bad CC attached?
Actually, I always make sure there isn't any CC in my game (and on my Sim) before I launch and whenever I download some Sims from the Exchange they always wear the same spare clothes (depending on age/gender).
//Edit: makeups (excluding face paint) and bracelets are the only optional CAS parts which have default replacements
//Edit2: Before you use a mod, go to "Plan Outfit" wait a minute and click on accept. It may be that in CAS mode the items are checked for validity.