So think for a minute how do you get new customers? If your answer is referrals - this may work for now but what happens when your referrals dry up (and eventually they will).
Or maybe you have ads out in different mediums - like the yellow pages, newspaper ads, billboards, radio ads, - in other words, traditional marketing.
Can you tell if your ad is bringing you business or do you consider it a needed expense? Ask yourself this, what would happen if you shut that ad off - would you see less sales?