And with invention of Betting exchanges now you can trade bets just as in previously mentioned financial markets. To be able to trade you need to register at some betting exchange, Betfair betting exchange is most popular and it's recommended for beginners.

Now after you're done with register process be sure to check Back & Lay in that way you can see both - Lay and Back bets.

If you ever tried Live betting you'll know that Odds are always at movement. This can be exploited buy back bet with higher odds and sell it(Lay) later when odds are lower. This is called trading. After buying and selling bet you're not risking to lose any money anymore, you can only profit. You can guarantee risk free and only profit situation. Of course profits will be much lower compared to simple bet which is left to the end of match. But it pays back as there isn't any risk to lose money.

To learn more about trading and get some trading examples read full Bet Trading article