Part of my marketing strategy is to ask new customers where they heard from me.
Rather than saying 'google adwords, or 'my google search found you on yell's website', they'll often just say 'the internet'. So, I'm never too sure which on-line campaign is working best.
Joe, maybe a potential customer sees your web based booking system, thinks you're a good, professional company, and calls you anyway (rather than use the booking system).