As far as I can tell, they are not a legitimate company. There are just so many scams perpetrated in the name of 'mystery shopping' that it is often difficult to tell who is who. At the same time, common sense tells you that if they are offering big payments to new, untried-by-them shoppers or offering to pay up front for work, the chances are really really really good it is a scam. The OP (original poster) did not mention how they heard of WC or anything else, so it is impossible to be absolutely sure.