First of all, any scams that want you to cash a check and sent Western Union or money gram. Valid Mystery shopping websites don't ask you to cash a large check for them and then send it by a money gram or western union. It just doesn't happen.
Also, when you receive a notice from a valid mystery shopping company that you are contracted for. Put their website in your browser bar and then log in. Do not use the link in the Email. Occasionally, con artist make a fake website. Then if you click on the link in the email. Look at your browser to see if it is the correct website. More than likely it is not. Like the fake paypal sites well conartist are doing this with Mystery shopping sites. It is better to type the URL your self in the web browser or when you sign up with a mystery shopping company save their home page in your favorites or bookmarks.
If you find that you have received a scam by email, go to your email settings and where it says how emails are read. Check the header so that if will appear in the email.