JacobJ's post pretty much tells it all.
In my years of shopping I have never been paid up front for any jobs, though I understand that if I was taking on a very expensive job with some companies with whom I have been working for years that could at least be discussed. $100 per hour is pure bull. Most mystery shopping you are doing well if you make minimum wage for your time involved. And always you need to be wary when strangers come to you making offers. Companies I am signed up with will send me offers I can accept or reject on a job by job basis and companies with whom I am not yet signed up may suggest I go to a legitimate, secure website, to sign up with them.
Don't fall prey to the 'too good to be true' type scam out of wishful thinking.