You can actually get as many gems as you want for free, everything you have to do is gain levels. I like to call this cheat "gem mining", because you have to work to get the free gems. Its really easy and has few steps. First, you need to open the friends tab, then you click "invite friends". Now's the trick, instead of writing a friend's e-mail adress, you can write your own. And soon you'll recieve an ourworld invitation. Then, on the e-mail press "go to our world" and it will bring you to the home page, there you have to click "not a member" and join again. When you reach level five with your new avatar, you'll recieve five gems for your old one. It is important that you go to your e-mail with clicking the "go to our world" because otherwise you won't get gems. And you can make new avatars again and again and get as many gemms as you want, it's your choice.