I have not seen this offer. If I did, I would snigger and delete.
Who's the MSC?
No, no and NO!! Anyone who is successful with mystery shopping--able to keep to a schedule, do their bookkeeping, follow directions, write acceptable reports--is worth more in the 9 to 5 job world than minimum wage and would more than likely be receiving benefits such as health insurance, paid vacation days and sick days, workers comp, promotions, raises etc. Why be an 'employee' 'on call' 9AM-9PM 7 days a week? You are likely to work less than 30 hrs per week so they can claim you as part time and eligible for no benefits.