Studies 3 & 4 were conducted entirely with undergraduate participants taking a laboratory class for course credit.
Studies 5 & 7 were done entirely online. It's not clear how participants were recruited.
Study 6 was done by recruiting volunteers through Craigslist with a "chance to win" a $50 gift card.
There's a lot more here to make me skeptical of any conclusions from this "science".
EDIT: Here are the first three tested "unethical behaviors" from study 4[1]:
1. Use office supplies, Xerox machine, and stamps for personal purposes.
2. Make personal long-distance phone calls at work.
3. Waste company time surfing on the internet, playing computer games, and socializing.
They get a little worse, but it's easy to see why some "upper class" respondents might measure as "more unethical" in this survey: Employers who predominantly hire high skill workers for high salary positions generally don't care about these behaviors and employees act and respond accordingly. Does Google consider it unethical if you photocopy a few "Lost Dog" posters?
[1] http://www.pnas.org/content/suppl/2012/02/22/1118373109.DCSu...
EDIT2: Oh god. And as the link danielweber supplies below points out, study 4 wasn't even run with real participants from different classes, instead, "We adopted a paradigm used in past research to activate higher or lower social-class mindsets and examine their effects on behavior."
That a paper like this can be published (and funded by the NSF!) seems like an awful reflection of the state of the social sciences.