When you buy seed get feminized seed so all you get is females (ok there is the chance of hermies). Without very costly genetic testing you cannot tell until the preflowers form (at around 5+ weeks). Sometimes you can pick the male from its growth as they get taller faster (with more stretch between nodes and go single node faster) than the heavier setting females. Bag seed is pot luck you get what you get, sometimes it works out, sometimes they are boys or hermies. A lot of time and money to invest in not a crop, bag seed can be a good learning tool, or just a fun grow (when you have plenty of weed). I myself dont recommend bag seed unless you do not need the weed.