This is actually pretty easy to track. Your web site marketer should have your pay per click advertising campaign set up so that when someone comes to your site and makes further inquiry, either by requesting a book or free report or by filling out your contact-us-form, that you know that they originally clicked through your Google or Yahoo ad. In other words, your pay per click, like all other marketing, must be trackable. This is easy to do from the webmaster's side, but you need to be sure that you have an offer of some sort at your site because eventually when you do work for the client and make some money, you should be able to go back to see exactly how it was they found you. This is true whether you're running a Yellow Pages ad, a TV ad, or a Google pay per click ad.