he didn't say it would hurt your campaign, he said it would hurt your quality score. What he means is if you have an opt-in list on your site, google gives it a lower quality score so your clicks cost more. This doesn't necessarily make it a bad thing, as you will probably make more sales with a good list. What I'd do is make like a 7 page ebook, with enough content so that they get some information and think its helpful, but not enough that buying the ebook is worthless. In this free ebook lets say you suggest some workouts or something, then say in your ebook (the one for sale) you have complete workout plans. Just an example. Now that you have a list, you can send them some helpful articles every so often so that you gain their trust. In these articles you can promote other products you want to sell (only good ones) or not. Then when you release your next ebook, you will have built up a relationship with your list, send them out an email and you already have lots of customers.