you can also lay odds-on bets, which will not risk that much but where you could land a larger amount if the odds-on bet (for the punter) loses!
similarly on BetFair you can often stake a quid (for example) on a 100-1 shot, and if the price moves in, say to 50-1, you can take your pound off the table and have a 'half-bet' left for free, or clear your entire bet for a double-your-money profit. On one pound staked none of this is too exciting or profitable, but if you had staked more you can see how trading around positions on BetFair can give you a much more profitable profile than a simple bookmaker's shop.
I was laying odds on NFL games a few years back - sometimes in the last minute where the ball was dead or going to be and it was a virtual certainty but some people still had money hanging out there I could take. I had a nice looking position with the SF49ers v The Cardinals and looking to clear up something like $50 for about 30 seconds left in the game, when something odd happened and the SF49ers got the back off Arizona and not only scored a touchdown but also a 2 point conversion (which they had to do or else I'd win my bet) and I saw about $1,500 leave my account. That was a not-so-good result, but my girlfriend at the time was with me at a party (a business one) a few days later and had a few too many beers to drink. Then she blabbed to someone of importance (who had a very conservative outlook) that I had gambled and lost this amount of money on a football game - not quite the image I wanted as a serious business pro in that company, ehehe.