Caveat to my wasted effort comment:

Your'e an e-commerce site that has a problem with people buying goods (especially virtual goods, ebooks, gift cards, etc)[1] with stolen credit cards. You need a solution.

The hardest thing I've ever had to crawl (as I mention in another comment in this thread) has been linkedin and Facebook. Why? Because I have to be logged in to get the data I want.

If you want to stop crawlers you can also put the good stuff behind auth, but you need a solid auth mechanism. You can't just do email verification because I'll use shit like https://www.mailinator.com to generate a ton of fake emails to sign up for your site.

[1] Why virtual goods? You can't stop shipping or track down the person once the card is reported stolen.