When buying vintage lingerie it is always wise to take your measurements.  Also, allow some extra room so that the piece will fit you comfortably.  Make sure that you look at the description and ask any questions that you might have.  Do some research because that is a wise thing to do before making a purchase.  I have noticed that in particular some sellers with list an item as 30s but it really isn't a 30s item at all.  Ask questions.