The terms "legal" and "illegal" really are terms of are with respect to a criminal matter. The question that you are writing about would not be a criminal issue. Rather it could be subject to a presumed contract assuming there is one by the retailer mandating that the items be sold solely at home parties and not in a retail environment.If the seller has purchased the items from a vendor and there is no contract prohibiting how the items can be re-sold signed by the seller, he or she can do whatever she wants to do with the product such as selling them in a retail store location.