Summary: A listener wants to know why Ticketmaster charges a convenience fee if you want to print out the tickets you buy online. After all, it's your ink and paper, and you're not asking Ticketmaster to mail your purchase. Economist Emily Oster of the Chicago Booth School of Business has been decoding the universe for us, and she's got an answer for you. It's got to do with the network effect, locking up a market and — of course — supply and demand. If you've got an economic riddle for Emily Oster, e-mail it to us at planetmoney@npr.org.
