What shape is your funnel?
Put random folks in at the top and loyal customers come out at the bottom...
A billboard leads people to a website, which gets some people to subscribe via email which drives some folks to respond to a promotion which leads a few to come back for the stuff that isn't onsale, which leads to someone who can't live without you.
That's the obvious path of outbound marketing. Most people you pour into the funnel hop out long before they become loyal customers.
The thing is, some funnels are more efficient than others. Expose your idea to ten of the right people and it catches on with three of them. Other ideas or offers need to be exposed to far more people (and go through more steps) before they're likely to convert someone.
The mistake we often make: thinking that the problem is that there's not enough people starting the process, not enough people being exposed to your offer. In fact, it's almost always a problem with how efficient the funnel is and how likely it is that loyal customers tell their friends. If you take care of those two elements, you have a lot more to invest in promotion, and delightfully, the promotion is more effective as well.
Google advertising puts the funnel shape under stress. If you can make your funnel more efficient, then you can afford to spend more money on each person you put into the top of the funnel via a paid ad. If your competitor can convert twice as many people as you can, she can spend twice as much per person, no? And thus the smart competitor will buy up as much of the market as possible. The only response: shape a more efficient funnel.