Craigslist Scam warning

I received an email recently that said: "Dear Applicant,



     It’s great hearing from you from,reviewing your resume we got for
the job of Mystery Shopper Position as posted on Craigslist.
Mercantile Systems,Inc. is a company that conducts surveys and stealth
evaluation of companies and organizations. Our mystery shoppers pose
as normal customers to perform specific tasks such as purchasing a
product, asking questions,registering complaints or behaving in a
certain way and then providing detailed reports or feedback about
their experiences.)
It included a place to put all of my information on the email then hit reply!

They did a great job making it look like they were responding to my email. It stated everything but the time I sent the email. The date matched something in craigslist I did reply to. But knowing I would not respond to a secret shopper ad unless by mistake I was fairly certain I did not reply to it. Sure enough, on the 8th I replied to one ad on craigslist. It was a customer service ad that said nothing about a secret shopper. The persons (?) name matched the one on the email I received. So I fired back at them that they were crooks and how I figured that out. I keep careful track of what I do online. I didn't tell them how I do that. Why help them get better at what they do!
This kind of scam goes like this: They give you an assignment and tell you you will receive $$$$$$$$+. When you are done with it and submit the results they send you money via paypal or Western Union. They then file a dispute with paypal and get their money back, or you end up finding out the money from Western Union was never good in the first place.
Pay pal has no proof the work was done. They have no choice but to refund the buyer. The Western Union check IS NOT Western Union!
You may get the "money" before you go to your assignment.
On a final note-Never give any information on any email directly and hit reply. These people are also spammers and worse yet, the primary sources for information for identity theft!
These people are getting tricky and are very creative in how to disguise themselves as legitimate employers!