Hello and Welcome!
I would be wary of advertisements on Craigslists - most advertised mystery/secret shopping jobs are scams. However, you will find a tremendous amount of legitimate work through this forum. For instance, at the bottom of this page is a link to a list of over 200 mystery shopping companies - which are all legitimate. The 15 most discussed companies (another list found with the same link) are all larger companies that offer work nationwide.
This is a great side gig for parents looking to make side income and need the flexibility to take care of their kids. You'll find this forum fairly active and if you post questions, you'll likely get several answers in short order. There are folks on this forum of have been doing this for more than 20 years. Most folks do this part time to supplement their incomes. Some do this as a way to enjoy more expensive recreational activities. A few shop as their full time work.
Hard work builds character and homework is good for your soul.