Please go to the work at home/employment scams section of this message board and read the info on Secret Shopper Scams post there.
Have you reported the post to Craigslist?
Also, when you go to the website listed in your post, http://www.shoperslink.com
, you will see the logo for the MSPA. If you do a Google search on the MSPA you will find their REAL site. Looks like the scammers are now making copies of the MSPA site. I would report this to the MSPA and they may want to see the emails and the full headers from those emails.