I am not familiar with mysteryshoppingonline.com. I do know that there are a bunch of rather questionable 'shopping' opportunities that require that you register with a whole bunch of websites, sign up for free trial memberships and ultimately end badly as if you don't end those 'free' trial memberships in a timely fashion your credit card will be charged and because you have registered with all these sites, they now have an 'existing relationship' with you that allows endless phone calls even if you have a phone number on the 'do not call' list. Be very careful.
If you wish to try mystery shopping there is a list link at the bottom of each page of this forum to our "Official List of Mystery Shopping Companies". These are companies that actually exist that we work with.