Read this ... carefully!
http://www.fdic.gov/consumers/consumer/news/cnwin0607/scams.html
Extract:
"In these cases, the depositor most likely will be held responsible for the entire amount of the fraudulent check."
Instead of cashing the check or sending it back, take it and the envelope in which it came to the post office. They will use it as evidence and pursue the scammer.
I received a text message, stating they wanted to order Mary Kay products. I sent them to my website and then received an email. The emailed me stating they were going to be in my town for a photo shoot and gave me a list of items they wanted to order. She then asked for my address and info to send check to. NO THANKS!!!