I don't quite understand it, but my understanding is that you can virtually purchase whatever you want (almost), but taking delivery or actually owning it may be illegal. Has something to do with your representation as a purchaser, i.e, are you a "legal purchaser", a seller cannot necessarily determine if you are a legal purchaser unless they are required to do so by law, so the assumption is that you are legal. It probably has something to do with jurisdiction in terms of sales/commerce, etc. Someone with the background could certinly answer better. EXAMPLE: you go to a liquor store to buy booze, you are supposed to be 21 years old. The liquor store asks you if you are 21, you say yes (but you are only 16). No proof of age is required by law, and you look 45 years old. Who has performed the "illegal" transaction?