Questions like these come up all the time and they get a ton of stupid replies (no offence intended to anyone). Really. It's down to skill. Like everything else in life. That usually comes from practice and lots of it + talent.
PLENTY of people are making TONS of money buying traffic. Can someone who's never bought traffic before make a profit in the first go? Absolutely not (unless they do something nasty like selling malware of course), you will loose a lot of money to begin with, unless you have an experienced and talented media buyer sitting next to you, teaching you the ropes.
That's why mainstream companies pay a lot of money for experienced people to handle their advertisement and why big companies have their own in-house guys...
