Ok, newbie question alert
Isn't this where the infamous 'list' starts? You have your customer from PPC, they obviously fit your marketing profile because they have purchased from you, and the theory goes that if they have once they are more likely to again. Therefore isn't your next step to keep in touch via a newsletter (if they have consented) so that you can guide them to other products you have that will interest them?
I can't think of any other ways other than the newsletter/informative email of keeping them in touch with your products, or am I missing something?