"Craigslist is not only gigantic in scale and totally resistant to business cooperation, it is also mostly free. The only things that cost money to post on the site are job ads in some cities ($25 to $75), apartment listings by brokers in New York ($10), and—in a special case born of recent legal trouble—advertisements in categories commonly used by prostitutes, because authorities encourage vendors to maintain a record that would aid investigators. There is no banner advertising. They won't let you join them, and at this price you can't beat them either."
http://www.wired.com/entertainment/theweb/magazine/17-09/ff_...
Usually, when companies get mad about scraping, it's because it's either bypassing the ads that make them money, or in rare cases bypassing a premium API. Here, PadMapper is doing neither.
In fact, if Craiglist is so committed to not updating their ugly website, why don't they just license out a public API, killing two birds (new monetization strategy and having a better interface for free) with one stone?
Though to be honest that makes no sense, because that's exactly what they're getting from the third party site, and they're paying for that...
Edit: Not sure why this comment is getting down-voted, but if I offended some one that was not my intention.
Once you have a web site that attracts buyers, you can replace craigslist data with your own listing service and stop paying for their API.
They clearly don't fear this kind of competition in the mobile space, hence offering licenses for mobile-only API use.
PadMapper is basically a pointer to a listing on Craigslist (when Craigslist listings are the reference), where you can search the pointers with filtering that you can't on Craigslist. In order to get to PadMapper, you have to visit the site directly.