Never heard of them but there are many companies that use Secret and Shopping in their names. Quick and dirty reality checks:
1) Did you find them or they find you? Legitimate companies rarely go out soliciting folks unless you are signed up with the Prophet 4 system and gave them permission to give your email to other Prophet 4 companies.
2) Do they have a website where you are signing up to work with them or are they asking you to send your demographic information via email.
3) Are they offering to pay too much? Most mystery shops pay fees in a range of $10-15. A $250 offer from a company you have never worked for automatically fits in the "too good to be true category". Generally you even have to earn your right to do jobs paying more than about $15 bucks by consistent reliable reports for work done with the company.
4) Are they offering to front you 'expenses' for your work? That does not happen with legitimate companies except in very very rare situations with shoppers they have dealt with for an extended period of time.
If after the quick reality tests you are still interested, googling the company name reveals nothing and googling the individual's name yields nothing that would imply mystery shopping. (A film makeup artist, a climate change activist, and a 93 year old UK female with a MySpace page are not promising sources of mystery shop work.)