The first thing I would recommend is to look up GCS by their website and find out if they sent you the cheque. I hate to say it but it is unlikely. If you didn't sign up to shop for them on a website then it is almost impossible that this would be a legitimate situation.
I would also call the bank and tell them you are the victim of a scam and maybe they can stop the cheque from going through. Finally I would call the police and report this. I recommend doing all this first thing this morning.
Best wishes and let us know how you make out. Mystery shopping is legitimate and GCS is the name of a real company. Unfortunately a lot of criminals use the names of real companies to make themselves more believeable.
Edited 1 time(s). Last edit at 03/25/2015 01:00PM by Bena.