I think the search needs to be for mysteryonlineshoppers (i.e. the plural). A recent thread is [
www.mysteryshopforum.com]
This thing rears its head from time to time and if I recall correctly you are sent a list of websites to register with and then another and another and another and . . . well you get my drift. After your have completed your 100 registrations or whatever the heck it is, they will pay out the $20 you have earned.
Meanwhile all of those free trial offers you had better keep track of and go back to cancel if you handed out your credit card information or they will charge your card because your "free trial" period is over.
Typically an individual is paid a hefty fee (compared to what they are offering you) for each customer they send to register. As their providing affiliate, the guy who sent you may earn $15 while you are paid 20 cents and only once you have registered with enough companies. So they earn $1500 before they will pay you your $20.
I will leave it to you to decide whether this is 'legitimate' or 'business' or 'market research' or 'fair to anyone' or 'survey' or just plain old scammy.